your question is a difficult one.
My overly simplified answer may not be of help.
Traveling about as I do; I can go into about any ?country store? and purchase .22's-.38-.357-.45 without too much sweat.
When I'm looking for .380's-.41's-sometimes 9mm: it doesn't happen.
Standards are available without ?big city? shopping.
Walk-abouts require forethought and reasoning. My reasoning, simplifications.