Thank you for your question.
These are our offers for international guests: International guests | SBB
A 6 months period is already considered more of a permanent stay. We do not have a specific offer for tourists staying half a year because we already have a lot of offers for permanent residents: monthly oder yearly travelcards, passes for specfic regions and so on.
I suggest you purchase the normal half fare travelcard anyway, because its cost is quickly amortised.
For personalised counselling, meeting your needs and requirements, I kindly ask you to call our SBB Contact center (+41 (0)848 44 66 88, CHF 0.08/min, available 24/7) or to visit any SBB ticket counter.
Kind regards and happy new year