The Sector 7 shops are located on the Sector 7 slums in Midgar. Cloud can visit the shops after his first mission with AVALANCHE either before heading to 7th Heaven or the next morning before embarking on the next mission.
The Sector 7 Weapon Shop is the only location the Iron Bangle is found, so they must be bought prior to the Sector 5 Reactor attack to avoid missing them since the shop becomes unavailable after.
During the time the Turks take over the Sector 7 pillar there is a man selling items by the fence, but the normal shops cannot be visited.
The Sector 5 shops are scattered around Sector 5 Slums of Midgar. Cloud can visit them after meeting with Aeris and later when returning with Tifa and Barret to visit Aeris's mother. The shops can be revisited on Disc 2 onwards after finding the Key to Sector 5 from Bone Village to return to Midgar, but they won't have any new stock.
Wall Market shops can be visited when Cloud and Aeris visit the place to seek entrance to Don Corneo's mansion, and later when Cloud, Tifa and Barret want to climb the wall to the upper plate. Wall Market can be revisited on Disc 2 if the party finds the Key to Sector 5 from Bone Village to return to Midgar. At this time, the man in the back of the weapon shop has a new accessory to sell.
The man at the back of the weapon shop sells Batteries when Cloud, Tifa and Barret visit the shop on their way to climb the wall to the upper plate. If visited from Disc 2 onwards, he will sell a Sneak Glove.
The Shinra Headquarters shop can be visited when Cloud, Tifa and Barret first infiltrate the building to save Aeris. The shop is in the bottom entrance lobby before taking the elevator to the top floors, meaning the party might miss out on the shop if they take the fire exit stairs instead of barging in through the front doors.
When the party returns to Midgar in Disc 2 to stop Professor Hojo's evil plans, they can find their way to the headquarters from the train tunnels and visit the shop to open the treasure chests.
Chocobo Farm can be visited as soon after the party first leaves Midgar and can be visited any time after. It sells items pertaining to catching and breeding chocobos. On the first visit the party can buy a Chocobo Lure from the farm needed to catch wild chocobos. After obtaining the Highwind, the party can rent stables from the farm.
Junon shops can be visited after leaving the Mythril Mine and any time after. The shops change stock after the party obtains the Highwind, but because of a glitch, one of the Materia shops' stock never changes.
Costa del Sol shops can be visited any time after crossing the ocean on the Cargo Ship. Yuffie Kisaragi mans the Materia Shop on the first visit if she has been recruited but is not currently in Cloud's party.
Mideel can be visited after obtaining the Highwind. After the town is ravaged by an earthquake a lot of the stock is lost, but can still be purchased from a profiteer at the far left side of the screen near the doctor and a nurse, albeit for inflated prices.
Chocobo Sage runs a store that sells chocobo merchandise. His shop could be considered a secret shop as his cottage does not appear on the map. His house can be found in the northern regions of the world after the player acquires the Highwind.