Stockyard

Rockstar's Ultimate Edition text puts Stock 305 in Stockyard, and that is the only place the district is named. The store itself has official renders, two people sitting on a hand-painted van in Stock 305 clothing, but nothing in them establishes where the neighbourhood sits or what else is in it.

Stock 305 wears the Miami area code as a brand, and a district called Stockyard sits naturally next to it: the industrial, warehouse end of a coastal city rather than the beachfront. Rockstar has confirmed none of that, and no street sign with the name has appeared on screen.