Hero Outdoors is a good place to find boots, and a variety of other gear and clothing you'd need. But if you're on a tighter budget, general outdoor stores are also a good bet. Places like Sporting Life, Mountain Equipment Co-op, and etc. are pretty good places to look.
I got a pretty decent pair (Oakley SI Assault Boots) at SVP Sports Outlet for like 1/3 of its original price.