I like James gaskets which are readily available for original knucks. The only issue you might have is the "rocker tins" which are actually aluminum. FHP near the end used red hi-temp silicone underneath (between the head and the cup) and Permatex Ultra Grey on the top covers. Of course if you are running a big-bore stroker the head and base gaskets will be different but should still be available.
Don't know if S&S is selling parts yet - got tired of asking with no concrete response (and I am a dealer). Have a set of FHP heads here in the shop waiting for parts availability so I guess I should start calling again
Your situation does not surprise me. Nothing but grief with the final FHP (before S&S took over).