Be a Pistolero, take two weapon fight, two double pistols, and rapid shot (and pre-reqs). At 11th level take signature deed (or w/e it's called) and place it on the bonus deed you got from becoming a pistolero. You'll also need rapid reload and alot of alchemic rounds.
Using the double pistols special each shot can shoot 2 bullets, since it's now a free action to reload and you only need to possess 1 grit point in order to perform the deed given to you at first level.
You can fire 3 times a round off of your normal attacks + 1 from 2 weapon fight + 1 from rapid shot which = 5 shots. Each shot is shooting 2 bullets so 10 shots a round. Say you miss with every shot 10 * 3d6 / 2 on average = 45 damage a round WHEN YOU MISS ALL OF YOUR TOUCH ATTACK SHOTS. :P Have fun.
You are about to start a new campaign.
You need to pause the world and have the same conversation, GM and players, as you would at the beginning of any campaign. What kind of setting is this, what themes will you envision tackling, what's your playstyle?
It sounds like you started in a "typical" magic-but-low-tech setting. The setting has now changed. This is no longer your old campaign. Your group needs to decide whether they are interested in playing a new campaign: magic-tech. (Something like the Age of Legends from the Wheel of Time, perhaps?) You need to have that honest conversation with them about whether you want to run that different campaign and whether they want to play in it.
(One possibility, as @SSD correctly points out, is that your PCs are now Misunderstood Villains.)
Or not.
Or the cannon works only once, for reasons. But the real reason in that case is that you didn't want to run a different campaign and you decided not to. In that case you should be honest with your players about what happened.
But notice, you're already having these problems.
You wanted them to play the movers-and-shakers game where they allied with the kingdom, worked the NPCs, and ended up with an army.
They explicitly told you that this wasn't interesting and pulled off an (awesome) end run.
You and your players are playing different games already.
So talk about it.
An historical reflection.
I grew up in a version of D&D where PCs past level 10 were expected to be movers and shakers in the world. Your magic-users were magic-makers, your thieves had entire cities under their control, your fighters were barons and dukes, your clerics had followers spanning continents. They reshaped the world map through magic and through might of arms. The game naturally required transition, in my experience, from one of small-group adventuring to one of collaborative world-building.
Or you started a new campaign with low-level characters and a few familiar high-level NPCs hanging around in the halls of power.
This power progression of the classes--particularly of the spells!--is baked into the DNA of D&D/PF versions. Your PCs--all magic users!--are powerful enough to be affecting the world. And as you say, the world's noticing. It may be time either to pivot or to semi-retire these PCs.
Best Answer
It's very difficult to play a character who can't see, especially at low levels. Not only will you not have the perception bonuses to pinpoint someone (DC 40 to find the exact square of something you can't see before applying modifiers up or down), and getting a way to "see" all the time is just as difficult.
Also, if you don't take the Blind-Fight feat, you'll also need to deal with the DC 10 acrobatics check to move around faster than half speed.
Thankfully, there are a few ways to get an ability to help you find your opponents. If you're an Orc or Half-Orc, you can grab the Keen Scent feat, letting you notice enemies within 30ft of you most of the time, and letting you pinpoint the square of adjacent enemies. It's not great, but it'll at least let you pick a square to roll your miss chances on instead of taking a 1/8th chance of even swinging in the right direction.
There aren't any feats that grand blindsight or blindsense, sadly. There's a dwarf-only one that gets you short-ranged tremorsense, but it's higher level than you can use.
This leaves spells and items, really. Echolocation grants 40ft blindsight, but is a higher-level spell, and so, it's probably out of reach. Same with the shapeshifting spells that grant blindsense.
Looking through the pathfinder SRD, there are a few items you could use, but they're probably all outside your price range. Still, I'll list them. Maybe your DM is nice and will give you one.
"Sense" abilities
Blindsight
... I hadn't realized how hard it is to get blindsight in Pathfinder. Honestly, I think if you're looking for an item, the best bet would be to ask if you can pull the Blindfold of True Darkness from 3.5's Magic Item Compendium. 30ft blindsight for 9,000gp instead of the exorbitantly priced stuff in official PF materials.
Other than that, I guess the best choice is to figure out something with your DM. Fighting blind in Pathfinder is hard, especially at low levels... I wish you luck, in any case.