Turns out, there is no shop, really. Rather, there is a dude standing in the streets of Baldur's Gate that acts as a shop. No icon on the map. No bubble over his head. No hints from NPCs. Nothing.
To the designer of that little feature, thanks for wasting my time.
Back to your post on the 13th, what you should check out is the original "Baldur's Gate" (http://www.bioware.com/games/baldurs_gate/) for the PC (and Mac) using the infinity engine.
"Icewind Dale" was a more dungeon-crawl focused game, but I think they'll suit what you're looking for -- full party based systems, full towns with NPC's and quests and reasons to go to them, and an overworld (and some guest NPC visits) that ties in with D&D from your P&P days (if you played Forgotten Realm).
You should be able to buy them online at Amazon or various Mac gaming sites.