383 Tunnel Ram?????

There's also the option of making your own.

You should be able to get a sheet of gasket material from your local parts store, though they may have to order it.

Something like Fel-Pro 2498 may work, though you may want to look at some of the other compositions.
http://www.oreillyauto.com/site/c/detail/FEL0/2498.oap?pt=N0488&ppt=C0137