At least two oracle mysteries contain revelations letting an oracle use his Charisma modifier instead of his Dexterity modifier to compute his AC (the mystery lore has the revelation sidestep secret and lunar has prophetic armor). I want a revelation like that, but I don't want to take the mysteries that make available that kind of revelation. Is there a way for an oracle to get an off-list revelation?
[RPG] way for an oracle to gain or take a revelation from a thestery not his own
This is a pretty interesting question. Without more clarity as @mxyzplk points out, I'll keep this at general suggestions, but I'll be happy to add more clear suggestions later if necessary.
First off, let's look at your ability scores. Your Cha 20 is going to be netting you +2 additional 1st level spells per day, which gives you a total of 5 (I'm going to leave 0th out of the answer, since they're however many times you want). Problem with Oracles is they get 2 1st level spells known per day at 1st level which if I'm not mistaken can't be modified by anything. This is also going to make the saving throw target number for your 1st level spells 16 (10 + Cha bonus of 5 + Spell level 1), which isn't too shabby.
Your Revelation makes your Cha bonus apply to your AC instead of Dex, and adds to your reflex save. You're going to be decently hard to hit, with a +5 bonus to your AC and reflex.
The rest of your abilities, though, cap out at a +1 bonus. So base, you're at a +1 to hit in melee (+0 BAB for starting Oracle), and a +0 for Ranged.
You're getting 4 + 1 skill point per level for the Int bonus, +1 for being human (and possibly an additional one if you do that with your favored class, which I'm assuming is oracle). The rest of your stats are +0.
The Lore mystery will play heavily into your skills. You'll be doing a decent amount of skill rolling outside of combat, and will be able to identify magic items with the best of them. Plus, being able to Brain Drain a captive to get information is just cool.
The Trickier bit is going to be combat. Here are a few suggestions to get you started:
Okay, so here's where we can branch out a little. My primary suggestion would be (depending on the composition of your party) do something with buffs/debuffs. Bless is a nice 1 min/level spell that gives every ally within 50 ft a +1 attack bonus and a +1 to fear saves. Couple that with your high-ish spell save DC and you could take Bane,Cause Fear, or Doom for a bit of early-on battlefield control. Your High Cha will give you a decent save DC, and additionally your AC will be pretty decent for your class. Also since you can Spontaneously cast Cure Spells whether or not you know them, you're a decent support healer in a fight as well. You can also up your Save DC with Spell Focus in the given school your chosen debuff spell is in.
If you want to go the route of attacking things youself, I would suggest you take Magic Weapon and Shield of Faith (or Bless if you want to up your attack more, it stacks with the Enhancement bonus of Magic Weapon). You can take feats which make you a bit more effective with your chosen weapon (which, base, is limited to simple weapons), but you need BAB of +1 to get Weapon Focus, and you can't get anything past that without being a fighter.
Alternatively, you could take Summon Monster I and a few feats to boost the effectiveness of the summon (Augment Summoning and it's prerequisite), to dole out some more damage.
TeeHee you can't hit me
If you want to do nothing but dodge attacks, you could: Take a combination of Entropic Shield, Shield of Faith, and Protection from Evil. Note that the AC bonus of Shield of Faith and Protection from Evil don't stack, since they're both deflection, but you get the idea. Nothing like a 20% miss chance from ranged attacks and a 20 AC at 1st level (+4 from armor, +4 from Cha, +2 from Spell). If you consider upping your Dex to 13 at the cost of say your Con, you could take Dodge as a feat, get another +1 to your AC, and then make up for the loss of a hit point per level with your favored class bonus.
Per your Metamagic Feat suggestion, since you're a spontaneous caster, keep in mind that any metamagic feat you take will force you to spend a full-round action casting the spell. (Aside from Quicken Spell, of course).
From someone who has never played Pathfinder, but a fair share of D&d 3.5 :
First things first, I'd drop the 12 STR. 10 should largely be enough for a troller, I might even go all the way down to 8 (especially with your specific curse, thanks to which your load won't matter much). These points will be much better spent in INT (you never have too much skill points) and/or WIS (to negate the sens motive malus the 8 brings. A negotiator needs as much Sense Motive as he can get).
By first party (made by Paizo) RAW, no there isn't.
Extra Revelation requires that you have the prerequisites for the extra revelation you're getting (which means you have to have the appropriate mystery).
Ring of Revelation also explicitly states that you must have the appropriate mystery to use the revelation contained in the ring. (And the commentary on the sidebar is an unofficial (albeit from the Creative Director) statement saying that Use Magic Device would not allow you to fake having that mystery prerequisite)
There is, however, a third-party feat that would allow you to do this:
Strange Revelation enables to you to use Extra Revelation to acquire a revelation from a mystery that isn't your own.
Third party stuff is a grey area, and something I recommend you ask your GM about before you take it.
TLDR: No, but third party content allows it.