One cog might be that there are too many pharmacies for suppies in Greece if they're truly on every corner.
That said, we know there have been shortages here for a couple years. A couple weeks ago I was at Walmart to pick up some basics and saw many empty shelves. Had to ask the pharmacist where some simple everyday OTC things were only to find out they had them behind the counter. She claimed she hadn't had time to put them out --- uh, no, stockers do that, not the pharmacist. I noticed they only had a handful of each item still in their packing boxes so that didn't make any sense - like they were intentionally holding them back and selling only when someone asked about them.
I'm guessing shoplifting issues rather than supply issues.