Theoretically, you can use all keycaps that fit CherryMX or Gateron switches. I once had the Hype X Pudding keycaps on it, but I wouldn't recommend them because they don't light up nicely (because the switches only have one LED on top and not two). The choice of keycaps with a CH layout is unfortunately very limited here, but if you don't mind taking a US layout, then just make sure they fit on CherryMX or Gateron. Doubleshot would also be an advantage, as the keycaps then wear less quickly.