It may seem too simple, but I would have someone Swiss German speaking call Feldschlosschen directly and ask them if they have a service that would be able to help.

They may be able to provide you with kegs directly and the beer taps/tables used for large private functions. They should have plastic glasses as well (good idea vs. glass bottles with a large group). They might have some big banners as well that you could put up as advertising for them (and might help with the negotiations/pricing). You might find that this is the easiest and least expensive option.

Do this before running around to all of the retail outlets.