Is there an OTC treatment for ringing in the ears?

No. Lots of stuff on the market, but none that I have seen work.
Not really. Some people state they get relief from vit b type combinations or riboflavenoids. But it doesn't work for a lot of people either. The best therapy is reconditioning or masking therapy - check out www.Beyondtinnitus.Com for the newest web based therapy (no relation to me).