While there have been a few, controllers that use microswiches are extremely rare. Even if you can find one, it'll probably be the switches mounted on a circuit board underneath.
What do you plan to do with this? If you have a larger enough area, you might be able to adapt a full-sized joystick to do this. Or scratch-build something that uses standard microswitches as the mechanics of a joystick are very simple. Precision would probably be your biggest challenge there.
I agree the NGPC stick was awesome. Actually the whole NGPC was awesome. I still play mine sometimes. SNK vs. Capcom wouldn't be half the game it is using a gameboy's directional cross.