Available at any local Reformhaus or Müller... It is called Melasse in the German speaking Switzerland. I have some in the cupboard in the kitchen. Good luck
Funny you should mention this - the Bider & Tanner bookshop (!) at Bankverein has it. Go upstairs to the Englsih book section and there's a small selection of food there, including black strap molasses. I bought some myself the other week...
Black molasses is also often sold in drogeries or the larger apothekes that have a health food section (even though, yeah, i know molasses is not health food).
You can find good molasses at the American Store in Geneva and Nyon. I use it to make baked beans, and to make molasses butter to slather on corn bread.