If you can't go on the days open to the public, you can sometimes join a tour. We went in November, on a tour arranged by the Bosque del Apache. A man who observed the explosion led the tour.
http://peachfront.diaryland.com/newmex3.html
Scroll down a little, you'll get to the Trinity report. Pictures too.
Rives, I believe the tour guide told us that the tiny pieces of trinitite were selling for around $30 and that none of them were legal or officially acquired, even in the area gift shops. However, they don't really seem to mind. It isn't like the Petrified Forest where they promise that a curse will fall on your family for untold generations plus you could be fined thousands of dollars for taking or selling a specimen. I think I'd rather have the specimen than the $30, just for the historical value.
People interested in atomic history should also visit the National Atomic Museum in downtown ABQ. Highly recommended.
http://peachfront.diaryland.com/atomicmseum.html