Quoted:
Is there a secret place to buy these things? I would love to have one, but then again I think we all would.
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If you are talking about registered, transferable Colt M16A1 stripped receivers ...
There is no secret place to buy them. Because they do not exist.
Prior to the manufacturing-for-civilians cutoff on May 19, 1986, Colt had a policy since they first bought the design from Armalite to not sell to the public. One reason was that they made a business decision not to pay federal excise tax (usually 11%) when they manufactured M16 family full-autos, since military, law-enforcement and export guns are not subject to that tax.
Colt only sold via U.S. military contracts, foreign-country contracts, and directly to LE via contracts or through law-enforcement distributors for smaller sales. (Colt would terminate their relationship with any distributor which sold full-autos to qualified civilians.)
Given that all M16 sales were to military or .gov/LE agencies, they did not offer stripped receivers, only complete guns. In fact, when the U.S. military needed replacement receivers, Colt would not supply them, and .gov had to turn to outside suppliers like Balimoy.
Now, with Colt, you should never say never ... and thus there probably are one, maybe two unbuilt stripped receivers out there. No one knows. If they do, indeed, exist, as a rare collector's item, my educated guess is that each would be worth in excess of $50,000 to collectors.
So if ya want to, post a WTB on the boards. Who knows?