Keycap sizes are pretty much standardized. The only thing you will need to keep an eye out for are your modifier keycaps (enter/shift/space/backspace/bottom row). Those are measured in “u” where 1u is an alpha key, so your modifiers might be 1.25u or 2u or the spacebar is 6.25u/7u normally. So when you find a keycap set you like just check that it includes the right number of mod sizes.

I took a quick look at the Hades68 keyboard and I couldn’t find a specific link but I think this is the same sizing (from a tofu65)

So for looking for keycaps they will generally have a list of the keycap sizes. If you go to https://kbdfans.com/collections/pbtfans-in-stock/products/pbtfans-frontier for example you can see in one of the pictures it has all of the u sizing listed on the keys.

I would guess 95% of keycaps sets will fit 98-99% of standard keyboards (60%-75%) with anything over 75% needing an additional numpad add-on set. Unless you’re getting into some of the weird formats like 40% or ortho you probably won’t need to worry too much.

Hope this makes sense. Let me know if you need any other clarification.