The Stealth F16 uses a standard 49er daggerboard. Any 49er supplier could sell you one.
I think the later Stealths has a specific board and not the 49ER which the early boats had. Length was the same but very different in chord width.
I have a spare wider 49er style board which is sitting in the back of the garage which I could sell for not a lot of money, where are you based ?