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...

Hi bill, awesome and thank you. Yes the address is correct. It's just going to take a while. Just let me know what I owe you. Kind regards Karl
Has anyone in the UK bought 50 and wants to sell me their spares? Or does anyone want to go halves (thirds?) on an order?
@Thomas Uchiha I'm having the same problem than you. My doubt is, I just noticed I bought an ON/ON button not and ON/OFF (non latching), would hear from the specialists if this would be the problem ....
Thanks guys
edit: just adding the link for the one I bought
Do you by any chance have instructions how to hook 'em up?
16.75 each? the 14 needed costs more than the entire MCP
edit: just realized there are 50 per lot, not 1
@moss196422 - that's the same vendor (Abbeycon) I got my switches from (and linked to above)! Guess they got enough interest from us to offer the green LED/black button as a standard option :)
https://www.aliexpress.com/item/32795957738.html?spm=a2g0s.9042311.0.0.26fd4c4dwJK78F
I was able to very cheaply come up with black buttons w/green LEDs. I purchased buttons with red LEDs (easier to find) and bought a bunch of green 2mmx5mm green rectangle LEDs. The switch easily comes apart by removing the black switch cover first (pliers or teeth!), then i used a jeweler’s screwdriver to push up on the white side tabs. Then used pliers again (ok, teeth...) to pull out the pushbutton. Pay attention to the cathode and anode by matching the bend from the red to the green. Install the new green and seat it with ur screwdriver. Clip the ends and reassemble. I did 16 switches in less than an hour. Paid $8-ish USD for 20 switches and about $3 for a handful of green LEDs
I also got my switches from AliExpress,those 5 digit displays can be bought at opencockpits,a few colours to choose from.
No worries! Please share away :)
They look the Business! sorry about the delay in getting back to you. This forum does not notify us of any comments unlike the others. Would you mind if i post this to facebook late to help others?