Any outdoor store will carry heavy cheap camp iron.

If you want the good stuff, hit up central Maine antique mall in Bangor. A vendor there has an incredible selection of old stuff, perfectly refinished, and it's reasonably priced.

Antiques USA in Arundel usually has some good stuff. One vendor there always has a lot.

The willows flea market in mechanic falls has some good prices

I have a business card of a guy who collects and refinishes... and judging by what he was buying when I met him, he probably has an absurd amount of stuff. I'll grab his info at my lunch.