Actually Choate never made the folders but rather supplied the folding mechanisms to Springfield and the made the stockd using USGI fiberglass stocks,Choate folding mechanims ,a small piece of angle-iron and a M-16 pistol grip . There are a few options : Reese surplus/Beretta/Springfield folder ,Mc Millan, Springfield /Choate folder and many Home built units .
All are expensive ,a SA/Beretta original will set you back $300-500. A SA/Choate about $250 to $300 and a current Reese surplus which are sold out will run $200-$250.I have no clue on the McM's but I do recall thgat they were $450 or so without the butt part and they must be bedded
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I hope this helps !
Mike