I had the opportunity to stop by
Main Gun Military Surplus today and picked up a few items. The store is only open Tues-Thurs as they do most of their business via the web or at gun shows. Also, it's a small space, so they aren't able to display very much merchandise; my recommendation would be to call ahead and see if they have what you're looking for before making a trip.
What they did have on display was well-organized and was of good quality; it's definitely not one of those places where things are randomly jumbled about. Also, the prices are, IMO, very good. I picked up an M40 mask, with bag, outer skin, hood, and sealed canister for $66 (on sale) and an ACH helmet for $99.
Overall impression: Recommended. They have a good selection of items in good condition for reasonable prices.
