You're going back a couple of decades with that. For spare parts, I'd imagine you'll have to cannibalise a boneyard of it, at least this side of a Taiwan/Hong Kong shop.
Value depends on its condition and whether it functions. There's a WE "God of War" unlicensed green gas variant and a CO2 powered version by Umarex (I don't know the OEM), both of which are readily available now so you should expect that to limit the appeal of the KWC version mostly to collectors. The Appraisals forum would be the best place to ask what it's worth, assuming you have one.