Well the spyder barrel threads would work but I'm not quite sure if cutting that thing off is such a good idea, seeing as the barrel is quite expensive and you dont want a broken gun out of it after paying that much. But if there is a way to fit it I was also looking onto a milsim barrel:
http://www.octanegear.com/index.asp?...OD&ProdID=3360
I also made a mockup:
