Hmm, I don't think there are any events that close to Zurich right now. But throughout October, there is every weekend a bigger event within 30-40km from Zurich. You'll find plenty of information on http://www.solv.ch
, but it is all in german.
Oct 7: National race in Stein am Rhein. Registration deadline has been, but there are open courses where you can register on-site.
Oct 14: Zurzacher OL
Oct 21: National race in "Wilen b. Wil"
Oct 27: regional event in "Safenwil AG"
Hope this helps