ok so I just mapped the Taiko mode keys to the top row of my arcade stick. it's slightly easier because the buttons are larger and more spaced out than ZXCV.
it's also confusing as hell because you see this line thing:

in the actual Taiko no Tatsujin game, you're supposed to rapidly smack the drum, but osu! won't register it if you spam both keys. you have to tap ONE key and it's kind of dumb.
still an ok representation, maybe if you can find a PS2 Taiko controller with an adapter it'll be better.
or you can find an arcade with Taiko no Tatsujin. downside to that is that they usually have a limited selection of songs (the ones my brother and I found in Singapore had iDOLM@STER songs and Ai wo Torimodose, so it's all good)