Bulletproof windows in GTA V (Singleplayer)
Solution 1:
Pretty sure the only "armored vehicles" attainable in single player are the Rhino tank and the Duke O'Death (DoD is only available to "returning players" and those lucky enough to actually spawn the "Duel" random event and get away with the car). You can't even buy the stock Karuma (non-armored) in story mode.