I don't believe that the Goodyear Marathon is available in those smaller sizes...radial construction only I do believe.

Check out: goodyear.com/rv/products/marathon.html

The Carlisle brand isn't bad for those smaller sizes. You can get the Carlisle USA Trail in a 4.80x12 or 5.30x12.

Check out: carlisletire.com/products/trailer/usa_trail/index.html

I'd buy them from Redneckshadrap.