JohnH if you can find a DIY plan on the net its not all that hard to do. My mates and I did our G-11's together in one afternoon. But the Vixen is a much more enclosed beast, have you ever found any instruction on pulling it appart.
From a shop point of view i Think Bintel might be the best in Sydney. Though they dont sell Vixen (to the best of my knoweldge), there guys there sure know a heck of a lot about scopes. The only other chap is the dealer from HK who often visits Sydney. William is a member here his old website is
http://www.geocities.com/tatsco/. I know he ventures down to Australia quiet a bit and maybe you can get his help on this, even if its instructions. I have found him to be remarkably helpfull.
Regards
Fahim