I and my partner plan to travel 2or 3 times to Switzerland over the next 12 months. Is it possible to purchase an annual half fare card; and if so where and at what price?
Yes, that's possible, please see here: www.sbb.ch/en/travelcards-and-tickets/railpasses/half-fare-travelcard.html. There are a few differences with the regular one month version for tourists (e.g. you have to provide a photo of yourself), but it offers the same discounts. Whether this is the cheapest option for you depends on your travel plans.
I hope this helps. Enjoy your trips!