Found a couple on Armslist.com
One in Alabama
armslist.com/posts/12623300/mobile-alabama-rifles-for-sale-trade--bushmaster-ar-10
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One in Florida
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armslist.com/posts/12333878/jacksonville-florida-rifles-for-sale--bushmaster-ar10-rifle-chambered-in--308-winchester
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they are out of stock everywhere check with the major auction sites like G(un)B(broker) and G(uns)A(merica) Remove ()

Mike, this is about as rare as hens teeth in the current market Sir. I would check on large gun and accessory sites like (6)un (8)roker and Armslist as discontinued and hard to find firearms and accessories show up for sale by private individuals and small shops. Just replace (6) & (8) with G & B.