For stock bolts, you’re going to have to go through the hardware aisle at Lowes or Home Depot to search for a replacement. If you have a copy of one of the stock bolts giving you problems, take it with you to find the right screw/bolt with the proper threading. Both stores (as far as I can remember) also have holes to test the threading of screws/bolts. Worst comes to worst, take the stick hardware (faceplate or stick base) with you to test replacement screws/bolts, too.
I’ve been lucky on occasion to find replacement screws for broken ones in two Hori joysticks. (And people here think it’s only Mad Catz that produces the occasional dud!)
Cheap zinc screws are used in the Fight Sticks and one of these broke in the Wii Fight Stick I modded many months ago. I fortunately got a stronger replacement with the same threading but with flat heads. It actually fit better than the stock Hori screws!!!
For my second Arcana Heart 2 joystick, one of the screws holding the joystick to the faceplate mount was broken. I had a heck of a time getting it out; I had to maintain pressure on the broken screw while I was unscrewing it! Again, I lucked and found a replacement for it at Home Depot. It screwed in fine but the experience also proved that the screw mount in faceplate mount was poorly manufactured, too. The replacement screw – identical to the one it replaced – had a hard time screwing in.