They are available from most all of the AR kit suppliers
Olympic Arms, Inc. - 16" 7.62 x 39mm Upper Conversion Unit
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Barreled Upper 16" 7.62x39MM Complete
Pre-Ban 16" CAR 7.62x39 A2 Upper, Bayonet Lug, A2 Flash Suppressor OUT OF STOCK M&A Parts, Inc.