where can I get bigger fin for standard FCS plugs

like putting lipstick on a pig, but would like to see if I can improve the handling of my Bic Mini-Mal with a bigger center fin.
After getting the 8'6" Torq longboard, I am now keen to experiment with different fin sizes on the other boards.
After getting the 8'6" Torq longboard, I am now keen to experiment with different fin sizes on the other boards.