I haven't seen then around this time of year. But in the spring / summer you will have no problem finding some in most of the shoe / sports shops. In the meantime try ebay or Ricardo!
Not in, and don't know Zurich, but in general terms, I still see the generic own brand Croc-type shoes in all the usual places -- Vögele, Dösenbach, and as suggested above, Landi (once you're out of the city).
Alternatively, if you have a friendly doc. or dentist, ask them -- they always seem to wear them and have a year round requirement.
Erm, no, they don't deliver here. Was just trying to get a pair of winter boots (man, they look so comfortable and warm!!) and was about to check out when I saw they didn't have Switzerland on the menu, and here's what they say:
"If your country is not listed in a scroll down menu, then it means we do not dispatch items to your country. Please do NOT enter a different country instead. Your order will be cancelled and a refund will follow a.s.a.p."