This is one hell of a crusade if been fighting for some time now, I found and ordered a set on Aliexpress. In order to match it to a GMMK Pro You will need to order 4 different config options, gladly they are all sold separately. 1 set of ISO-CH modifier, 1 set Mod Pro modifier, 1 Base set and 1 Modifier set, it will amount to a total of 55 chf. I managed to get free shiping and its surprising good quality and retro color scheme.
Here are the links:
Base set + Modifier + Mod Pro
https://www.aliexpress.com/item...
ISO-CH Modifier
https://www.aliexpress.com/item...

For ISO, check out:
https://www.wasdkeyboards.com/keychron-k...

For ANSI, check out:
https://www.wasdkeyboards.com/keychron-k...

You can also use the Keychron K2 chart as a guide (which uses a similar 75% layout) to learn about the keycap sizes you need.
ISO: https://www.keychron.com/pages...
ANSI: https://www.keychron.com/pages...

The unit of measurement for keycaps is expressed in U, where 1U is the size of a regular, square keycap. (So 2U would be twice as long.)

getting ch layout keycaps is super rare, the only store that sometimes offers it is Tai-Hao https://drop.com/buy... best is to follow their twitter tbh to not miss it

I recently bought this keycap set from Tai-Hao:

https://shop.tai-hao.com/products...

One of the only sets I found online which offer a Swiss layout. The quality is VERY good!
If you like the colors I suggest you give it a try.

Shipping is also quite fast.

I've made a list of keycaps I could find over a couple of months:

SA-P Keycaps:
https://www.pimpmykeyboard.com/

OEM Tai-Hao Hygge:
Tai-Hao Hygge

OEM Tai-Hao Blue Moon:
https://candykeys.com/product...

OEM Tai-Hao Miami Lights:
Tai-Hao Miami Lights

GMK (I couldn't believe it when I saw these):
https://candykeys.com/product...

Cherry profile:
https://kprepublic.com/collection...
↓
https://kprepublic.com/products...

Hope this helps and happy typing!

On drop.com there is a gmk laser set available at the moment. Although it doesn’t offer ch keycaps it has an expansion set with wich you could achieve at least a de layout

https://www.wasdkeyboards.com/swiss-deve... If you don't mind spending a little bit more money. You can customize the colour pattern too.

Hey there, if you are still looking for some CH-Keycaps... there are some available. See this Link: Glorious PC Gaming Race ABS Keycaps (CH, ISO, 105 Tasten)

Unfortunately, we do not have the CH keycaps. At the moment there are no plans to add to our range, I'm sorry.