Don't give up if you can't find a perfect one. When the gasket in my 30-year-old pump died, I knew I couldn't find another just like it. The guy at the local LBS had one that was a touch too narrow in diameter and about two times too tall. So I cut it down using a sharp pair of scissors, and then used a section of worn-out inner tube as a shim to make it the right size. Works perfectly.