Not exactly answering your question, however there is a fairly large number of avid cyclists on this board that have regular rides in the warmer months. Some of these are endurance atheletes of all ilks including some triatheletes (or wanna be's at least). Keep your eyes peeled to this site for updates.

Alternatively, there are plenty of triathalon clubs in Zurich (not sure any English speaking ones). I don't have a link at the moment if I find one I will post it.