In the process of changing the nose wheel tire on my 59' 172 I snapped the retaining ring clip that holds the hole bearing, washer, felt assembly in the wheel.

I can't find a replacement retaining ring to save my life... Online or otherwise.

Does anyone know of a Cleveland wheel STC for the early model 172s nose wheel? Cleveland seems like much better availability for parts as in finding out the hard way.

I know Airglas nose fork STC requires a Cleveland wheel but I'm keeping the stock fork.. for now at least.

Can't help with an STC for the nose wheel. My 57 C-172 has Cleveland mains on a STC, but it does not include the nose. For your existing nose wheel, you could try measuring the diameter of the broke snap ring and find a generic snap ring to replace it, or possibly call Alaskan bushwheel, Aircraft spruce has 2 different part no's for them that look like the correct part, see if either of them is the correct diameter for your nose wheel.