keep looking on Gunbroker. they come around often..
Try to get a No32 Mk3 that has the red W(waterproofed) and blue B (bloomed lenses) markings - the best of the bunch and possible for one man to zero on his own! Not cheap....but top of the tree
Earlier scopes (MK1) were prone to backlash issues and the Mk2 still required you to grow an extra hand and use the "zero tool" (which are normally long missing with the scope and the Ebay replicas tend to be POS)....a PITA!
You will also need to make sure that the scope you buy actually works...there are not many people left who can service them (as MJ1 says, Peter Laidler in the UK, Brian Dick in the US and maybe one or two others) and spares if needed are extremely scarce.
IMHO, given the above and the likely costs involved in returning it to functional condition a non-functional unit is probably little more than a wall hanger/curio these days so be careful.
Also, as MJ1 says....mounting these correctly requires a reasonably well-equipped and competent engineering shop. It is not a "drill, screw and hope for the best" gig.
This is a link to my clone build post from a while ago. My smith also has an article on his website covering the technical aspects of the build:
http://www.snipershide.com/shooting/snipers-hide-bolt-action-rifles/62417-brought-home-weekend.html
www.thamesvalleyguns.co.uk
Go to the "Armourer's Notes" tab and the No4T is the second entry on the list.
PS...MJ1...as always a lovely looking rifle beautifully photographed!