Those little black-plastic-and-steel momentary switches are basically universal. Unless you buy the most incredibly ****ing pathetic switch in existence, it'll be able to handle any power load going through an input device like a joystick just fine. Just get anything that fits.
The trick to electronics is that it's pretty much all only as precise as you care to make it. I have never, in all my years of repairing and building ****, had to do anything more than estimate what'd work for a given application.
Which has, granted, yielded some incredibly ugly hackjobs, because I'm too lazy to get any parts I don't have right on hand, but aside from aesthetics and the occasional thing you shouldn't touch 'cos I grounded the device to the metal housing, everything so far's worked.