I own one, I have had it for some 20 years, it didn't work when I was given it and it stayed that way until last week, when I decided repair it or spare part it. I found the valve seal was at fault; none available; so I designed a replacement set of bits, as I still can't manage to turn polyurethane with any success. It took a couple of attempts, but the gun now works ok but seems a bit down on power from my memory of trialling one in the early 80's; I need a genuine rear sight [hint], but in the meantime I have an Anschutz one fitted. I now just need range time to check its accuracy and at the moment - - - sorry it's not yet for sale. I will update with range results when it happens, time is not on my side at the moment but it will get fitted in somehow.
Regards and good luck with the search.
abellringer