This achievement is luck based because the gold bar doesn't always spawn but this is where you can find the safes.
the safes don't always spawn in the same places, you'll get a mix of the various spawns.
Time Out (Coffee shop)
-One small safe behind the main counter
-One large safe in the back room in the wall
Kung Bo (Antiques Store)
-One small safe under each check-out counter
-One large safe beside the rear exit
-One large safe in the back employee's area
Pear Store (Electronics Store)
-One small safe under each side of the check-out counter
-One large safe in the back room
Twenty-Four Seven (Corner Store)
-One small safe behind the main counter
-One large safe in the back room