I am not aware of a definative work on IJ or the Enforcer, as there is for Colt, Walther, S&W, Browning, and other firearms. There is some collector interest in the early revolvers but never for the Enforcer series. There really isn't that much interest in the gun. The big problem is that the parts are not interchangable with U.S. military M1 carbines and you can buy a real M1 for under $400 and put a folding stock on it and it turns out being only about 5" longer than an Enforcer. Sorry I don't have any more info. I can tell you that at Texas gun shows you can buy them for as little as $250 and I have seen them priced at $450 for NIB, but I have not seen any sell at that price.