In building an MCP based on Karl's design, I had a real hard time coming up with a good source for the specific KD2-22 buttons required (black button with green LED). Finally, I reached out to several vendors on Aliexpress who carry similar buttons, and was able to find one that was willing to make the specific type for me. Just in case others are looking for a good source, here's the link to the specific vendor/switches I found: http://s.click.aliexpress.com/e/j7c8F5I
They don't show the black/green buttons, so you have to contact the vendor (via chat) and make the specific request. They were willing to do it for me if i ordered 2 lots (100 switches), but that's still a good deal (comes out to ~$0.45/switch with shipping to US).
I got the switches and they seem to be of real good quality (good strong "springiness" in the momentary action), so I'm happy with them.
Now, to find those 5-digit MAX7219 LED displays Karl found, only ones that will actually ship to the US...