There're at least two ways...
The following let the barbarian actually rage using his own kind of rage more often than normal. "Whirling frenzy is otherwise identical to the standard barbarian rage" (UA 66), so these should work with that, too.
The 2nd-level Drd spell blood frenzy [trans] (Spell Compendium 33) causes 1 touched creature to rage as if it used its special ability rage normally "but this rage does not count toward the creature’s number of rage attempts per day." Note: Rage attempts?
This is likely the best choice, equipping an ally with a wand of blood frenzy (2nd-level spell at caster level 3) (90 gp/charge) and the barbarian himself with a potion of blood frenzy (2nd-level spell at caster level 3) (300 gp; 0 lbs.) in a potion bracer (Sharn: City of Towers 158, 159) (100 gp; 1.5 lbs.) for emergencies (that is, if the DM's not ready for the ready-drink helm to enter her campaign.)
The shoulders slot item mantle of rage ("New Magic Items" 2) (6,000 gp; 1 lb.) grants the wearer, if a barbarian, the ability to rage 1 additional time per day, and, if not a barbarian, the ability 1/day to rage like a level 1 barbarian.
...And a clutch of edge cases
In addition to the 3rd-level Sor/Wiz spell rage [ench] (PH 268) et al. (which isn't really rage but a buff spell with attached penalties), there are a few lesser alternative sources of barbarian rage not involving taking levels or feats.
- The gutworm (Fiend Folio 220) is a symbiont that at will can cause the host to "enter a frenzied state identical to a barbarian’s rage" for 4 rounds, but this rage explictly provides bonuses like the typical level 1 barbarian's rage. Note: More rage, but not the right kind of rage.
- The face slot item mask of fury (Dragon #324 76) (12,000 gp; 2 lbs.) 2/day grants the wearer the ability to take either a free action (if he's been wounded within the last hour) or a standard action and deal himself 3 hp of damage (if he hasn't been wounded within the last hour) to enter a rage "as the barbarian ability." Note: Whether this can be a barbarian wearer's own rage or must be the rage of a level 1 barbarian is the DM's call.
- The supernatural ability past life (DMG2 159-60) has one option that 1/day can grant the possessor the ability to enter explicitly a greater rage as a level 11 barbarian. This special ability is nominally for NPCs and has a (ridiculous) Level Adjustment of +5. Note: Probably too late for this barbarian and too stupid for any PC (or, for that matter, any PC's follower or cohort).
Yes, that last scrapes the barrel's bottom.
The best way that I can see you improving your combat effectiveness is through the specific spells you choose.
As you had said, money is sort of tight in your campaign, so you need to make due with what you have at your disposal naturally. Luckily, this isn't hard considering that you have a +4 Cha score (Giving you anywhere between 1-4 additional spells per day at your current bonus). So considering your want to improve how well you do in combat, focus on preparing combat buff spells
These are the spells that I think you should prioritize (keep in mind that I only have the core rule book on hand):
+Bless Weapon(1st): A very situational buff, but powerful when used against the right enemies (ya did good on this one)
+Magic Weapon(1st): Prepare this instead of Bless. Bless may give you a bonus against fear, but Magic Weapon increases your damage as well as your attack bonus.
+Bull's Strength(2nd): I know that you put most of your stuff into Ranged Weapons, but everything on the list available to me is either a buff you don't need or something that seams too underhanded for a "rock star" (also, I don't think you need a spell that lets you take half of the damage that your friends take when there is a fully-functioning tank). As you may already know, Bull's Strength increases your Strength Ability by 4, so at the very least, you increase your Combat Maneuver Scores. This means it's easier to absolutely wreak an enemy's day by affecting how they move, inflicting statuses on them, or simply moving through them.
+Greater Magic Weapon(3rd): THIS is one of the key spells you should prepare when you get into the upper echelons. It's like Magic Weapon, but it gives you additional bonus amounts for every four levels your character has. Also, this spell specifically states that you can cast this spell on up to 50 arrows in the same quiver; this means that if you have to switch to another bow, or if your party also invests in bows, the spell is used to its maximum potential between multiple weapons.
+Prayer(3rd): Anyone in a 40ft radius of you receives a +/-1 to every roll depending on their loyalties; That's an increased advantage of 2 against whatever enemies you are fighting!
+Dispel Chaos/Evil(4th): these two spells give you +4 against the attacks of the designated alignment and automatically dispels effects cast by said creatures or spells that are of that alignment
This last one is just in case you attempt to build physically or your Fighter is being cornered by a Demon or something...
-Holy Sword: PROS: weapon automatically becomes +5 AND deals an additional 2d6 damage to Evil Creatures. CONS: Can only be applied to melee weapons and negates the powers of whatever weapon it is used on (that last bit could be fun to use against an enemy using an all-powerful cursed weapon, but again, this is a bit situational)
I hope this helps.
P.S.: Your party should invest in Heavy Repeating Crossbows once you hit level 10
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Best Answer
The most common approach is to use Summon Monster spells to heal. You can increase your options for this with the "Summon Good Monster" feat. Here's a list from reddit; I've added an [SGM] tag to the options that require the feat:
There's also limited wish and wish itself, which can duplicate cleric spells for you.
The Samsaran trait "Mystic Past Life" allows you to add spells to your spell list. The trait says: "The spells must be the same type (arcane or divine) as the spellcasting class you're adding them to", but I guess some people argue that (for example) cure light wounds can be an arcane spell since it's on the bard spell list.
You could use magic items such as a gloves of first aid or a ring of spell storing. Each of these say in their description that they allow you to cast the spell yourself.
If you were playing in 3.5e you could take the Arcane Disciple feat and add healing spells to your spell list. That doesn't work in Pathfinder, though.