I'd say you would do well to buy from Henry, Carey, and Greg(That's IM, Beck/SE, and Vintage Motorcars Inc.). If you want an honest, straightforward experience, that is.
If you want to be messed with, call John Steele or Steve Lawing, you'll get what you deserve, you've been warned.
If you're looking for an actual kit, I'd call Doc Kleber at Kitman Motors.
Disclaimer: I've bought a roller and a semi-roller from Greg at Vintage. I've bought a bunch of parts from Beck/SE, and personally know Carey(and the boys!) and Henry Reisner and consider them friends.
I drove my Spyder today, it's been a few weeks or a month since the last drive. That sucker is quick! And comfortable as a Spyder can be. Thanks again Greg, for giving me a great base to customize to my liking!