I came across these two original frames in a parts deal - both from Michigan dealers and basically impossible to find as most were either thrown away or rusted away.
The first is from Stan Long Pontiac in Detroit, a well known performance dealer that sold the famous Super Duty 421 Tempest that was famously sold on Ebay a few years ago. This dealer also sold the Jim Wangers Blackbird RA Firebird. Items from this dealership are nearly impossible to find and I have never seen another license plate frame like this, let alone NOS. Asking $275 plus shipping.
The second is from Belcastro Pontiac in Ferndale, MI; this one is also NOS, but has some shelf wear as you can see in the pics. Again, this is 1960s-early 70s vintage. Asking $80 plus shipping.
Pics below:
