These are more tangential than direct, but:
The Wildlife of Star Wars: A Field Guide
The World of Kong: A Natural History of Skull Island
Star Wars and especially King Kong have pulp roots, and those two bestiaries are spectacular. Great art, imaginative creatures, lush detail, and much of that could be plopped into a pulp game. But to be clear, neither of these have anything to do with RPGs. They're just background material for the settings.
Edit: And if you're not aware of them, Grey Elf has a bunch of OD&D Supplement-style booklets. None are bestiaries, but there are three for Conan and one for Barsoom. May be vaguely related to what you're looking for.
https://www.grey-elf.com/ (you can tell it's old school because it has links to non-existent webrings)