They can be found on Keychron's webstore for $40+shipping but I think the better method is paying a few bucks more on amazon with prime shipping (if available). I've seen the price dip sub $40 (or at least at the time I purchased my set), been waiting for another sale to pick up a different colorway.

link: https://www.amazon.com/Keychron-Double-Shot-Cherry-Keycap/dp/B09V6WNBFP