Didnt see anything about this so here is what I have found out

After doing a certain amount of successful gang wars you get weapons delivered to your hideout
They will be in the TV/PC room down the hall from the save room [spoiler]and on the second floor of the second safe house[/spoiler]

Numbers represent the amount of successful gang wars

10 = auto pistol
20 = sawn off shotgun
30 = carbine rifle
40 = assault shotgun [spoiler]Must complete the mission for Elizibeta in which you ambush the drug van at the toll booth[/spoiler]
50 = grenade launcher
60 = nothing
70 = nothing

Ive only done 70 so if there is another to unlock I guess it will be pipe bombs at 80