Try Choppers US. I'm not sure of the metric/american conversions but he has 80mm and 100mm, if the rim you looking for is smaller, I'm sure he can still hook you up. Also pretty good chance your local bike shop can order you the size you want.
I'm running the 24" Surly Large Marge Rims. They are 65mm wide and with a 2.4" tire they will clear most balloon tire frames with a tad bit of clearance.