Off the top of my head there's:
Great Plains - http://www.greatplainsas.com/
Aeroconversion - http://www.aeroconversions.com
Revmaster - http://www.revmasteraviation.com
Better Half VW - http://www.betterhalfvw.com/ (2 cyl)

There's also HAPI and Mosler, but I'm not sure if either of them is still in
business.

Nope. They're gone.

You can also visit the Yahoo! group, AirVW:
http://groups.yahoo.com/group/airvw/

hth
J.D.
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