I was able to get some cast off airplane tires for free. They have to pay $5 each to dispose of them so were happy to let me have all I wanted. Now I need to find a reasonably priced 6" rim to fit. I am mostly on black top so the barrow tires we were using were getting chewed up. Not near salt water or sand a lot so they can be painted steel or galvanized.
Anyone have experience and a source for rims like this? Any help would be much appreciated.

http://www.gokartgalaxy.com/6_aluminum_tri_star.htm

If you get those wheels listed above, you will want to make sure to get the correct type of tubes or you will have issues.

The wheels have the hole for the valve stem coming out of the center of the wheel and it has very sharp edges. It is not thick enough to file down smooth so if you use a standard tube, it will cut the valve stem very quickly. The tube you need has a curved metal valve stem that will protect the tube against the side of the wheel but will also let you put air into the tube.