Speedster manufacturers are moving away from the VW frame because there are fewer of them avaiable in decent shape. As far as I know, the only US manufacturer that doesn't at least offer a tube frame option is Vintage (correct me if I'm wrong, folks), but even their's has a rectangular steel subframe added. Beck uses a 3" DOM round tube steel frame, while Intermechanicca (IM), Specialty Autoworks (SAW), and Thunder Ranch use Rectangular section steel tubing. JPS-Motorsports (JPS) still uses a VW pan, but offers a rectangular tube frame similar to Thunder Ranch's as an extra-cost option.
Check out:
www.beckspeedster.com
www.jps-motorsports.com
www.specialtyautoworks.com
www.intermechanicca.com
www.thunderranch.com
www.vintagespeedsters.com
Of these, IM's suspension is significantly modified, and SAW's is completely proprietary. Their Speedster is a mid-mounted Subaru with a double-wishbone suspension front and rear. Check all of these out at one of the spring kit car shows (Knott's or Carlisle).