Check my first post
here on the SPCR forums for a very quiet, very low airflow 60x60x10mm fan.
However, I really don't think you're going to find a quiet low profile 60mm fan with sufficient airflow to cool anything bigger than say 30W. Even quiet regular-height 60mm fans are hard to come by. I'd try a different tack on quieting your system-- try to get a short heatsink and then stick a full size 80mm fan on it. I don't know if there are any short/low profile heatsinks made to accept 80mm fans, but it will probably still work better than a slightly taller heatsink with a tiny fan.