awesome that you replicated the keyboard! the caps are custom made for us by FKcaps, we also resell them. the price is a bit high at the moment because we don't have a lot of excess stock https://shop.mntre.com/products/mnt-pocket-reform-keycap-set-100-pieces
i also have STL files somewhere and FKcaps might have sold some to other shops, you could ask them.