Gday Graham - I got it from Ron at Sirius Optics in Brisbane - they are an Optek delaer (there are probably others but I am not sure). I forget cost but it was around $350 (worth every cent) but I know he had had it for a while and his costs were lower as the $ was pretty good when he got it. I imagine they may be a bit more expensive.
I dealt with OptCorp direct in US re the adapter. I use an Orion Starshoot Pro 2 and the closest I could get was for a SBIG that uses a T thread. Obviously the distance from the reducer to the CCD plane is critical in the reduction ratio. Mine worked out close to (small fractions of a mm) the SBIG T mount one. They were really helpful in finding the right one. Mine is at:
http://www.optcorp.com/product.aspx?...n%20mount&st=2
Hope this helps
MB