I also live in Switzerland, and I can't remember seeing any 27" tires being sold here. However, amongst the hundreds of tires that
veloplus.ch sells, they do stock ONE 27" tire - a 27 X 1 1/4 Schwalbe Marathon for 39 CHF (Swiss Francs),
see here, they are even listed as being in stock! Given this, I expect that if your local bike store sells any Schwalbe tires then they can also order this tire from their distributor for you. As stated above, do not try to mount a 700c tire.