I recently acquired a Link Technologies branded Cherry G80-0536 and it was missing the F1 keycap - given that this board has an R0 top row and the F1 key would be in a non-standard color (mod colored, I believe it is closest to the current GMK CB or possibly BJ), I really doubt I'll find what I am looking for, but hey, can't hurt to try.
So, if you happen to have an incomplete keyset from one of these boards or a Cherry board of similar vintage in the same colorway, and would be willing to part with your gray R0 F1 keycap, please let me know. Photos of the board attached.