Due to a humorous misunderstanding regarding a bedliner, I recently removed the factory bed tiedowns from my '97 Tacoma. They were very rusty, as were the screws - in fact, I had to use a screw extractor to get three of them out. The tiedowns I salvaged: I just polished them up on a wire wheel and then painted them with several coats of Rustoleum. (I found a can of black metallic flake in our model shop - I'll have the snazziest tiedowns around.) But the screws were a total loss.
I got some new ones (.52ea, not that horrible) from Toyota, but I quickly saw why the originals had rusted. The galvanizing, I think, is just cheap cold-dip and won't last. Also, they've got ribbed teeth which are supposed to stop them backing out (which it does, trust me) but would have chewed up my pretty paint job and more importantly would have exposed the bare metal on the tiedowns again.
A fellow I know advised me that these are just 8mm (also known as metric size M8) screws. So I went on McMaster-Carr's website (everybody should know about McMaster-Carr - they are the Industrial Supply Company of the Gods: