I have used
http://www.wheelbasealloys.com/
before to source wheels for my VW T5 with no problem in the past, in the UK.
For the price of having tyres changed I am considering buying a new set of rims & tyres and storing the summer set in the basement. I've spoken to wheelbase and they'll ship to Swiss (ad not charge the 20% Vat, I understand I'd be liable for circa 8% import tax when they arrive.
Is there something similar to wheelbase in the geneva area???