Sig has gone through some changes in ownership and is reportedly in the process of moving to a new facility. I've seen some people state that they have recently ordered form Sig but their stock seem pretty hit and miss at the moment. On a more convenient note the plans for the original Kadat (Mark I) are available on Outerzone. It is a kit plan so it doesn't show all of the different ribs but it would be a place to start if you really are wanting to scratch a wing.