Shelf stable bread was tested in 1990 and I was a guinea pig for natic. I think it came on line in 91 or so. The first bread was a small white loaf that could be cut in two to make a sandwich. Back then we had the ham slice so all you were looking for was the mayo. Sadly the ham slice left us in 2000.
Somewhere in the early 2000's they started making the round "burger buns" these along with the older style are part of the T-rat family and come packaged in singles and 6 packs. In the system they can be ordered separately or if you order certain T-rat items they are included. If your T-rat order includes a tray of BBQ pork 3 packages of 6 buns will go with it.
They have never been included in the MRE line. It is kinda hard to find in the surplus world but is not bad at all. All this useless information running around my brain.And officially they are good for 3 years @ 80 degrees. And as we all know drop the temp on MRE's and the life goes up.