Following the lead of amd6547, I'll tell you that I got my M12 holster and accessory shoulder harness at www.SurvivalCenterOnline.com
They are both Bianchi products with a NSN on them. There were several manufacturers of the M12, Bianchi being one. The site I mention is good for USGI equipment. I also purchased some M16 magazine pouches that were brand new but that is another story.