You could check Junkyards, but may not find one in much better condition, but then again, worth a shot.

You might be able to substitute one from another vehicle or something more modern. I have a Plastic Vapor-Separator for the fuel-tank on my '79 CJ-5 Jeep.

I'm guessing autoparts stores and/or junkyards would be potential sources.

In any event, I wouldn't count on the Charcoal-Canister doing the job. Also, seems like there should be a better solution than going to an "open" or un-vented system like they had in '68. It could work, but there might be other problems.