We have had A5s, B6s of several types by five manufacturers/importers, 0-8-0s in seeming abundance, the F1 by Gem, H-series in relative abundance, and the G5 by at least four suppliers. Even the 4-4-0 has been done at least once.
I submit that PRR has been covered in O scale at least as well as many other RRs, and way better than, say, NYC, SP, UP, GN, etc.