RE: Where have all the deltas gone?
The BTE Delta Vortex kit is still available, but currently out of stock. (It must still be popular, as they seem to sell out periodically and then re order. At least twice in the last couple years.)
I just got an Outlaw, but they only had the U.S. Navy version left in stock. They seem to sell out and reorder a lot, too.
I think deltas would be more popular if more guys understood their flying qualities- very broad flight envelope. If the wing is not too thick, they are very fast, but can be slowed down to a walk for landing because of the deltas ability to fly at high aoa.
I got into deltas with laddie Mikulasko's "Arrow". It has a thinner wing than his Northstar and is quite fast (90mph) on a 46. I recently got foam core wing panels for it from flyingfoam.com, and am building a second hull with electric power. The hull is really easy to build- just a great big box with an engine stuck on the back. The wings were the tedious part, and with foam cores, that becomes a non issue.
I like the Arrow so much that I designed my own land based fuselage with retractable landing gear. ("Bullet") It is loads of fun.
Deltas rule. I can fly my Outlaw out of a baseball field surrounded by fences, and yet it will do over 70mph and flies away by itself on launch on a Rimfire 25/4S.