VAT on car parts and car related stuff cannot be reimbursed (even with stuff like yellow signal vests - own experience).
Exception, if you do make a lasting change to the car, the parts will be billed without VAT (but not the work itself, which can however be reimbursed).
As I live close to the German border, I purchase the tires and get them changed in Germany.
I usually order it from Euromaster or ATU which have competitive prices. You can also get the VAT back on the tires, however you will have to pay the Swiss VAT if the tires are mounted on the car or if its above the import limit (300 CHF per person per day).
Same applies for the car service, I have been getting German VAT refunds as recently as 5 months ago.