For future searches, looks like the following will work.
XT M750, 4 or 5 arm, (square taper only, the M571 Octalink won't work)
Middleburn for XTR M952 (obviously)
LX M570 4 or 5 arm
The LX is the cheapest option and is available new from cyclestore.co.uk
http://www.cyclestore.co.uk/productDeta ... ctID=16490
Lock-rings for Middleburn cranks also work for the XTR M952.
edit update: I got my spider and had to file some material from the edges of the channel where the crank arm sits. Fitted the spider and tightened the lockring. I fitted the XTR BB and torqued it to the correct value. Put the crank arm on and torqued the bolt to the lower of the value ranges (35Nm?).
I've ridden the bike for months with no problems until now. I wanted to fit a larger middle ring so pulled the arm off and changed the ring. The bolt felt a little loose when removing but thought nothing of it. When I came to re-fit the crank arm I found that the lockring was binding against the BB cup. I don't know how this has occured because it's been fine for months, the new chainring was the same middleburn but with more teeth.
The LX spider is going to need some material removing from where the lockring presses against it.