I couldn't find anyone to supply one for my 164 Super, so I had one made up by Carasel at Morebank. Only rated for 750Kg (I think) but has been fine to tow a fully panelled bike/kart trailer - don't think I'd want to tow a car trailer though. This was six years ago, but it cost $450 plus the relay/isolater box to connect up the electrics without paralysing the computer/ECU.
I'd sell it to you if I could find someone to take the car! Anyone want a 3.0 litre, 24 valve 164 - it's automatic, but still lots of fun .....