Hope it's okay that I'm posting again in a week old thread, but I wanted to post an update for anyone coming across this thread in the future.
I managed to find a single sealed, brand new in box Pixel 7 Pro from a seller that claimed that while it was a T-Mobile phone, it was both carrier unlocked and OEM unlockable.
Both points turned out to be true, and I am happily exploring GOS on my new Pixel 7 Pro! So it is possible to find a new phone that is advertised as OEM unlockable, it just seems to be uncommon.