Nick,
As far as I know, no manufacturer ever made a specific hitch for the SVX as it was a low volume production car. However, I'm pretty sure that a class 1 hitch for another Subaru could easily fit the SVX (or be modified slightly to fit).
The best hitches I know for cars are made by hidden-hitches.com.
Class 1 Hitch for '93-'01 Impreza
Also, the following is a good read:
Hidden-Hitches: How to Tow Safely
Happy Towing!
-Chike