While we don't sell keycaps here at Keebio other than an ortho compatibility kit, we do have some vendors that we recommend.
A fun part of the mechanical keyboard community is that we're found all over the world. You can support folks from all over with your purchases, if you like!
If you're really burning to put that last sweet touch of keycaps on your awesome build, the website that has keycaps readily available stuff pretty much all the time is thocstock.com.
​NovelKeys keeps a pretty diverse array of keycaps. They range from a more neutral look to some of the intricate fandoms... like Star Wars! These folks are nice to work with.
​Drop has various in-stock keycaps for sale, in various profiles like SA, GMK, as well as their own MT3 profile. The MT3 profile keycap sets they have typically have ortho sets/kits available for them too.
​Keycapsss has some Choc Low Profile Keycaps available if the higher profile keycaps aren't quite your jam. They also offer high profile keycaps and ortholinear keysets.