I can highly reccomend Juan at One World Fins in Florida. I use his fins on all of my balsa boards, and on some restorations as well. Beautiful woodwork, clear glass beads, and bubble-free lay ups.
Another good option is Richard McCormick- beautiful fins but generally unglassed. I’m planning on ordering a couple of his fins as well.
Hope that’s a start, they’re the two best that I know of.
Paul Jensen makes fins as well, he and Richard are both Swaylockers.
If you want wooden fins that are pre-glassed (quite the time saver!) try John Cherry, he also makes very fine stuff. I can PM you his contact info if you are interested.
I’m with Ambrose. Make your own. When I first found Sways I was trying to make a fish(like everyone else, it seems). Found Paul Jensen’s site and asked him if he would make me some keels. He was too busy so I made my own. I still thank him, because if you enjoy foiling a surfboard you will probably enjoy foiling fins for it. You can do it if I can. My most satisfying boards are the ones I made that included fins I made. Mike