Only the gun's original manufacturer can replace it.  Essential Arms hasn't existed in almost a decade, so you're on your own.


atf.treas.gov/firearms/faq/faq2.htm#o7


(O7) Are replacement parts for grandfathered semiautomatic assault weapons and large capacity ammunition feeding devices subject to regulation under the law?

No. Parts may be replaced in grandfathered semiautomatic assault weapons and grandfathered feeding devices without violating the law. However, if the frame or a receiver for a semiautomatic assault weapon is defective, the replacement must be made by the weapon's manufacturer or importer. The replacement receiver must be parked with the same serial number as the original receiver, and the original receiver must be destroyed. However, a manufacturer or importer who is unable to mark the replacement receiver with the same serial number as the original receiver may seek a marking variance in accordance with 27 CFR 178.92. In addition, the permanent records of the manufacturer or importer should indicate that the receiver for the weapon has been replaced.

-Troy