u can get a mini gun on top of the san fierro side of the kincaid bridge if u have access to a jetpack and the third island, and u can find the sword(katana) in china town in a back alley
in gta4 i would like (after i beat the game) to be able to select your gang's weapons depending on how much money u have, like have 20% of your guys have uzies; 30% have shotguns; and 50% have M-4's