You will find them on 13.6-32 tires... maybe that helps when asking around for them...
The more common 11Wx32 rims can also be used with 13.6-32 tires.
There are two measuring systems, or actually three: first they had 12-32 tires which measured 32" rim diameter, and 12" width from heel to heel. Later, the measuring system for this same tire became 13.6-32 because the absolute width of the tire was measured, not the width of the heel.
Later there came metric sizes, a 520/65 R32 tire has a width of 520 mm, the distance from rim bead to wheel circumference is 65% of the width (65% of 520 is 338mm) and the rim size is 32" from heel to heel.
Older tires with no aspect ratio mentioned, are standard 85% ratio height/width.