Hmmm. I don't know of any supplier for apple parts. However, Tankhobby had the idea, make new ones out of card stock. You may want to contact Tamiya USA first, though, and ask them. Worst they can say is no.
I never use a heat gun on plastic. Direct sun light, or sitting on a radiator (we still have them here) cooks them just right and the paint cures and dries rather rapidly.
I paint the fins with flat to match the tank it's going in. That prevents someone's shot from bouncing off a watch or some such and nailing my KT or JT to a cross with a ricochet.