I've been looking for the best part of 10 years, and haven't found anything else to fit.
It is actually a 6.75 x 1.75 shock I believe.
Even if you could get one the right length and stroke, the shock housing and position of the air valve tends to clash with the frame. Don't forget that you need to keep the fixed part towards the front!
On a thread on MTBR someone had a Tazmon fitted with a Fox Alps, but it turns out it was done before he owned the bike by someone who worked for fox, it had a cut down shaft to reduce the travel of a longer shock I think.
The only other option is to Heckler it, but that would miss the point of the frame entirely!
Risse Racing are still in business, and still make shocks to fit. They are also really easy to service.
I need to service my original shock, and the other needs a new shaft. I'm hoping that I can buy all the parts I need from Risse, although $200 for a new Genesis isn't too bad.
I have relatives in the US who will be coming back to the UK in the middle of January, who I shall be using to bring me back a new shock or some spare parts to save on the shipping fees. Let me know if you would like to add some things to my order.
Phill.