15484 posts
Hi Trappan,
You can buy the Swiss Travel Pass when and where you like, but online is more convenient and slightly cheaper. Please find all your options here: http://www.myswissalps.com/sw isstravelpass/price.
My recommendation would be to buy the pass online between now and a week before departure. You can print it at home and board your first train immediately upon arrival without loosing time.
385 posts
… and be sure to print out two copies of the ticket at home (if you buy online). On my last trip I lost my STP I think on a boat on lake Lucerne. Fortunately I had a copy and later continued on my trip to Zurich by train.