The SIG Primary Force is slightly different from Mike Pratt's original design. He wasn't employed at SIG when he designed it and at first presented the plane in Stunt News and plans were available through PAMPA at that time. Mike then produced short kits and sold them. The SIG ARF followed. Some years later Mike updated the design a bit and released those. SIG only did the one run of the ARF version because they couldn't find a reliable ARF company in China. PAMPA doesn't sell plans anymore, I don't believe, so that leaves finding one of Mike's short kits or copy of the PAMPA plan. There have been lots of plans and kit built planes over the years, so someone should have what you need.
Type at you later,
Dan McEntee