Hey, I looked around in OB for a replacement for your missing fin over the weekend, sorry, did not find one. Several folks knew what it was (LoxBox version side fin from Ace 6-Shooter), but didn’t have one. Best bet is to call LokBox at 760-757-3147 and see if they can help you out. If that doesn’t work, you can see if someone wants to make one for you, or glass one on, or replace the box…Good luck,