I did a bit of research and found it's even rarer than I first posted. Apparently, there were 3 production runs of 25 guns each...amounting to only 75 in the world. There were 2 versions - one with ABS stock (DX) and one with wood stock (Magnum) if my info is right.
If you're really interested, check with this guy:
His ebay store account is Raresoft, but his username at classicairsoft.net is "SniperX". He owns the upgraded one I mentioned earlier, and can probably find another. Hell, if the price is right he might even sell you his pre-upgraded one....