Depending on the car, you can try the
http://www.dayinsure.com/ which was recommended from my dealer in UK. I could not get a quote for the Audi i am waiting for. The answer was that they are not willing to underwrite.
What you also can do is to go to Strassenverkehrsamt and they will give you temporary plates. I think it is for max 4 days and cost 100 CHF. These are called Tagesschilder in german. The trick is, they are only third party liability so no comprehensive (Kasko) insurance is from them available.
I also talked to my insurer and he said that Swiss insurance companies won't give an insurance with foreign plates. I will clarify this as my car is ready for collect in UK and i am struggling to get a full insurance.