Slovak Fin Company – make great fins. However, remember to specify that the head (the part that comes into contact with your board) is flat. Otherwise, you’ll have to sand it to avoid the curved extremities pinching into your board when you tighten the screws.
Tarifa Fin Company – handmade fins that work out a little more expensive however the quality is excellent. Same deal as above for the head of the fin/s.
F-Hot Fins – produce carbon windsurf fins but if you want something bespoke these guys are more than capable of producing anything that you require.