I don't understand why different areas don't have certain cuts of meat readily available...I mean a cow is a cow right?? So why is any different in availability when they butcher for store shelves?
Probably for the same reason Suzi mentioned, if it doesn't sell, they won't carry it. I suppose things were different when butchers actually butchered their own beef and ordered it in by the side. Then they would have those cuts of meat if they didn't turn them into hamburger, but now more and more "butchers" order their meats in.
That said, I visted my local town grocery and they didn't even have LBs in the case, and certainly nothing labeled flank or skirt. They did have some NY strip loins for 2.99/lb and delmonico loins for 3.99/lb The delmonicos were labeled select, I could not find anything but the inspection stamp on the strips.