I worked with Airdale on these, they are the prototype of his design. I don't believe Airdale is in business anymore, unfortunately.
The main bows are made from 5/8 x .036" 4130 tube, with some 1/2 x .035" for the superstructure, with 1/4" UHMW (plastic) on the bottoms. I put a second set of Grove axles to the inside of the gear legs to mount them on. They work really well for the type of skiing I do. I may work on a tail ski when time allows.