They have them listed on their web page, under "Title 1" weapons, for $725 each.

http://www.usarmamentcorp.com/other_products.html

They also state that they have newly-made bayonet lugs for them, and if you buy 20 carbines, you get a rack for free! They look like they're in good condition.

I really wonder how they got them. Looks like it may be someone's collection.