2N3904 is a good basic NPN transistor, the kind electrical engineering students use to build their freshman and maybe sophomore level projects. I’d probably go mail order in a pinch.
You can buy a lifetime supply of 2N3904s on eBay for a couple of bucks. You can have ‘em in a couple of days.
I was talking to an engineer a few weeks ago and he told me he could switch 1 amp in a microsecond.
I said “wow, you can switch a million amps a second?”
Got that deer/dear in the shiny things on the front of the velocipede look.