I had the same problem with a Campbell Hausfeld, needing a belt, serpentine style (multi-v). I went to a local Grainger, told the same thing, but fortunately the company I worked for occasionally bought from them. Guy at the counter managed to get around me giving him an account number and I got the belt. Had to pay cash only.
Did you try MSC? They carry a lot of the same stuff that Grainger does. I don't know if they sell to the average joe on the street.