A good used one may never come available simply because the bumpers didn't protect the trim on these cars. The reproduction moldings are so outrageously overpriced that tailgaters will make you crazy.
There is a vinyl glue on molding from a Chevy truck that will substitute that 68 look though. For me... I would put the vinyl on both top and bottom, and put that good upper in a closet until a good lower did come along.
I waited over 12 years for a single piece of rear window trim to come my way. When I did get it, it was free so well worth the wait.
Good luck