MIDI buttons, HELP!

Hello to everybody,
I am a PhD student and I deal with the construction of new musical interfaces.

I contact you because I noticed that you deals also with MIDI
components.
I need some MIDI buttons in order to build a prototype of a
musical interface I am designing.
In particular I would need something similar to the MIDI buttons
of the accordions. So I can track which button has been pressed and with which velocity.


Could you please give me some information about such MIDI
buttons?

Where can I buy them? Do you have some technical detail?


Thanks in advance!

Cheers