with a few exceptions the full metal AEGs have not been legal to buy since 1998 and neither are the ones with black receivers. To be clear the black plastic AEGs are considered replicas and there is no legal way to import and sell them to the general public. As for the ASC retailers selling those black and metal guns, keep in mind the above and then you can figure out why other retailers are pointing out that their stock is legal
Airsoft guns with fully clear and partially clear receivers ARE legal so long as they stay clear as there is no way an actual firerarm could be made clear and as such they cant be confused as actual firearms.