Hotel Furian offers a course on a big public lake. Not many other boats there but very prone to wind and waves.
Volker Engelhardt, owner of Razor Skis, is skiing on a lake near Vienna (not by the name "Razor Lake" though). The club there - as well as other 4 ski clubs on private lakes in Austria - offers perfect conditions for slalom and will gladly welcome you as a guest skier.
bernhard kosch
secretary general, Austrian Federation