http://www.speednetllc.com/dbaastron...%20Focuser.htm
This one is made to fit and fit it does
I bought one and am very satisfied with it.
For the Aussies here, it is available from Andrews in Sydney.
FWIW , it looks identical to the William optics one and it appears to be constructed in a way as to fit different bases for different scopes, even SCT's