Don't sell your accessories. There are a couple of them that you can only find once or twice and if you sell them you won't get that award.
xRogue5x's forum posts
After you have finished mission 51 you can find them roaming around Grand Pulse's big central area. They are the same size as the other big ones except they have armor on their legs and the stuff on their back is a brighter silver color, also they have a prong like protrusion coming from their nose.
Asteroids, Combat, Scrambler, Super Cobra, Finalizer, Shaolin's Road, Yar's Revenge, Lunar Lander, Crystal Castles, Battlantis, Centipede, and Space Armada. I'll be getting some more, just enough to finish up my S rank in the game and after that just the stuff that I want.