You are right, there are few to none as far as manually adjustable. KONI is about it and they are WAY too pricey for this application. It wouldn't be hard to put the TEMS Actuators on the tops and wire in a switch. The TEMS actuators actually mount to the strut itself and not to the body or strut top. It would be an interesting conversion!
The best ones to use would be KYB AGX, but they dont make an MK3 strut. I bet with some trial and error we could find something that would work.
I found a few other candidates, such as DSM rear:
http://www.ecanfix.com/~aclifford/tree/images/index/mydsm/suspension/kyb/k08.jpg
also toyota tacoma rear bilsteins, 2000 celica rear, pontiac firebird rear, Mazda 80s FC3s rear, 87+ mustang rear, 82-02 camaro all have a shock with a similar bottom mount to the MK2, so those are some options.