If you ask at your gemeinde, when / if you have one already. In Zurich they are subsidised, you can join when there are still places available or at beginning of term. They can be a bit slow moving though. You kind of get what you pay for. If you want to learn at a good pace you would be better getting onto an intensive course. Classes are expensive enough here, and the quality of teaching varies enormously from course to course, in my opinion.