Try the Cheaper Than Dirt! website ... they have a 'Buy A Gun' link on the right side of their home page that is "designed to put potential buyers in direct contact with its national network of dealers who carry many of the guns that may seem hard to come by..." according to the NRA.
I don't know if this will work for you, but over the past decade & a half + I've also had good luck with the various online firearms-specific auction sites -- even bought GUNS from EBay prior to them going PC -- as always, do your homework and caveat emptor, but in many, many purchases I've only been 'burned' a couple of times and we managed to amicably work it out. And those couple of instances were for used pieces -- not NIB.
You know the websites I guess -- all the usual suspects.