I can recommend Spatz
in Zürich, near Hegibachplatz
. Their success is based on high quality cotton tents of medium and large sizes. They still make them and the big ones are really popular among Scouting groups in Switzerland. But they also sell tents of other brands.
Beside all the essentials for camping and trekking, they also have some fancy doodads like a dynamo-driven flashligh-radio-phone charger or survival food, p.e. can bread that is edible or a >1000 kcal brick with all the vitamins and minerals you need for a day
Generally prices aren't cheap but you get what you pay for!
There's also Hajk
, at Zürich main station and in Bern. Usually a bit cheaper. They are official partners of the scouts and the Jungwacht/Blauring, material related to the two youth organisations is available there, too, but nearly no fancy things.
You probably can order their catalogs online.