Joe,
?? maybe an "old school" salvage yard,
but I would say ebay or (as Chipmunk said) swap meets/Parts wanted forums would be your best bet.
I needed a Oil filler/Breather Cap, went to 4 junkyards/used parts/Pull-a-Part yard with no luck.
Not worth the hassle, bought one from Classic Parts, Kansas City for $3.95
I have the Manifold that came with my Core engine....I did look for you, but the Counterweight was missing.
Good luck, Jim
