I got those keycaps from aliexpress and the choice was purely based on “This is the cheapest I can find”, but they are quite ok if you don’t mind flat keycaps! I think about 0.2$ per keycap. (and you get free shipping after getting enough of them).
As for Ergogen, sadly I also didn’t find any. I imported and used the footprint exclusively from the Kicad PCB stage onwards. It took a bit more of manual work but was quite worth it! Hope someone adds it and the RP controllers eventually, it would be great!