HELP: Finding parts for ford 477/534 engine..

I used up all my resources trying to find a lifter valley pan gasket for our 65' F800 at work. It looks like they had 477 and 534 super duty engines used in these trucks. I would really hate to use silicon gasket. I have no leads. Anyone have one, know where to get one, or know whom to talk to? Any help would be great! Thanks!

 

If it still exists I'd bet these guys could find it-http://donstrucksales.com/parts.cfm

 

Have you tried some of the fire engine restoration sites? They put a lot of those engines in old Ford fire trucks.