best prices on everything! and they have every model of AR15 for sale, from the cheaper Bushmaster series, to the Colt AR15 which is the military version.
sells weapons modification kits.
sell shotgun modification kits, but they might have some AR15 stuff.
(FYI the AR15 you have pictured has an upper rail with custom sites, a tactical adjustable stock, custom fore-grip, and a choke-tube on the end of the barrel, which doesn't really do much for the weapon except look nice, but a choke-tube on the end of a shotgun will improve "shot distribution" AND allow you to stick the barrel on a door-lock and blow a hole through the door, without the weapon backfiring.)
All of these parts are available on the above websites
I did this to a 12 gauge shotgun, all from parts I got on these websites.
hope this helps.
Edited by KiLLeR SeNSaTioN™, April 2 2015 - 09:45 AM.