Oops... just re-read your post and realized that it's not the problem I thought - but it is still a solution for the chuck heads!
I went to damn near every bike store in Vancouver and checked a bunch of online sources as well when the rubber gasket for my Zefal Husky died for the 2nd time (the press-on presta adapter, not the thumblock operated schrader part). After failing to source the right part, I finally ended up buying a Silca "crack pipe" (disc wheel adaptor) and stuck it into the thumblock schraeder part. It works well for me, and cost me $10 as opposed to $50 for a new pump (Cdn prices).
Just another option for you...
<If you're gonna be dumb, you gotta be tough>
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