Replica 21FBP22 gaskets?

[old_tv_nut]

I note Doug Harland recommends re-using an old gasket after cleaning with soapy water and applying a rubber renewing product.
https://www.youtube.com/watch?v=VlWXNVJ5fN0

Now that I think about it, he may have reused mine AND applied tape to seal it or just hold it in place.

Unfortunately, you don't have an old one to reuse.
So, I hope you have luck in finding either an old one or a replica.