I am going to rebuild an old Shelby for my step-mother. It is her bike when she was a very little girl.

The tires and tubes have rotted off, and there are no markings on the rim. What is the best way to figure out what size white wall tires to put back on the bike? I measured from one bead to the other across the axle and it was around 22", but I didn't think that size was ever made. Any ideas?