
Adamantine Dragon |

I don't think it's going to be easy to find caveman sets at the proper scale. Most toy figures like army men are about twice the size of PF figures.
The easiest way to do this might be to find some barbaric fur-clad creatures, maybe troglodytes or even orcs, and replace their heads with humanoid heads and then paint them.

Lord Lazul |
Wow, this was a loooong time ago, but I found these recently which might help if you're still looking for these minis 6 years later.
http://www.stevebarbermodels.com/35-28mm-prehistoric-settlement
Hope you found what you were looking for! Reaper also has a few, though not as lot. Try keywords like "tribal" and "prehistoric."

Threadromancer |

Speaking of good for hill giants/ogres, maybe these Caveman Toys could also work for that sort of thing.
EDIT: if they weren't out of stock :(
EDIT Again: with a little extra blue/white paint at 2 3/4 in tall, the Viking Set might make some nice Frost Giants.