I haven't heard of a kit but I know how you could do this.  Get a later model
Audi Turbo with a 4 speed autotranny.  The automatic section will fit onto
the Vanagon diff.  Voila!  You now have a 4 speed auto tranny.
Would probably cost a bunch of money unless you did all the work yourself and
then I don't know how the gearing and shift points would match the waterboxer
(might be better for a 5-cylinder Vanagon conversion).
Ken Wilford
Van-Again
John 3:16