But the Rebel rifle isn't based on the M16, but the STG44.
There were two version of the prop. The one from ESB used by the rebels on Hoth is based on a sturmgewehr 44, but the one from RotJ used by the Endor Strike Team is a hacked about M-16/AR-15/whatever you call it.
As such, I feel any picture of an M-16 family rifle with no magazine inserted can be a reference for Rebel weaponry.