eHobby Asia have a good list of the Dytac Water Transfer M4 Metal Receivers for you to pick which camo pattern you want for your AEG. These cost US$104.00 each and these have aluminium die-cast construction. The packages include the following: Dust Cover, Bolt Cover, Hop Up Chamber, Recever Pin Set, Forward Assist Knob. So check them out.

DYTAC Water Transfer M4 Metal Receiver for AEG (Digital Desert)

DYTAC Water Transfer M4 Metal Receiver for AEG (Digital Woodland)

DYTAC Water Transfer M4 Metal Receiver for AEG (ACU)

DYTAC Water Transfer M4 Metal Receiver for AEG (Multicam)

DYTAC Water Transfer M4 Metal Receiver for AEG (A-TACS)