Plastic handguards or rails with covers? They are both available in green.
If you mean standard handguard, there are both M4 and carbine sizes. Cav Arms makes nice ones, there are cheaper ones available, but they are usually of lesser quality. Broken handguards are sharp, and tend to break at the worst times while managing to impale fingers. RRA also has some, but the green furniture from RRA tends to be different colors, and some that I had looked grayish black.