I'll keep my eyes open in flea markets, etc, but highly unlikely anyone would actually try to sell such lovely things.
Personally, I EXPECT to see displays with security items on them, and the monofilament thread sewed onto a big backing makes sense. And security cameras, why not use them? They are tiny and most can't see them, or if they are seen, so what? Those of us who don't steal for a living or for whatever reason, don't mind having them around. I would expect this store to start having such things now.
What about posting pictures of these quilts IN THE STORE and giving an award for their return? Were they marked by the maker? Or had the store's name on them? Could they be legally sworn to in court? I know I could instantly identify any I've ever made, and even still have the same fabrics left that went into them, plus pictures. And pictures of those quilts in process of being made, after taken apart, and after finishing. I think that sort of identification would stand up in court.
And the store DOES intend to follow up on this legally, doesn't it?