The law is broken by the importers. You can't expect all retailers to check the "legality" of every item they buy, but they may be culpable. Some retailers and importers have been responsive to letters from lawyers and it seems Jazz Factory has stopped pressing the Mingus record (at least it no longer shows up on the Blue Moon site). The problem is the cost of getting a law firm to do this is greater than the "potential" money saved. The creeps count on this.
On the other hand, I understand it is hard to resist some of these packages. JSP's package of Son House, Furry Lewis, Bukka White, Ishman Bracey and Tommy Johnson keeps calling to me. SHIT!