Just google up Steel Wheels Toyota Tundra and you'll find what you need.
I found:
http://www.partsgeek.com/gbproducts...ase&gclid=CMOnk7vK_sgCFZJbfgodCyoHUAAlternatively, I think the cheaper end wheels for the factory tundra's are pressed steel, not alloy. Craigslist is bound to have them for you.