One of the things I could suggest, particularly for the Flying A, since alot of older gas stations stuck around to become newer gas stations or were repurposed into all and sundry, is try looking for signs to place in front of/over the Flying A insignia/Signs. There are loads of older buildings that get sold and reused, and certainly around here there are tons of older service stations that are similar to what you describe that have simply been re-purposed into other things (Auto-Mechanics business' for instance). Anyway, just takes some imagination to repurpose assets in this game.
Good Luck
Falcus