Automatics:
(lv.1) Tommy Gun:
(lv.2) MP38: Florida - Granados Compound - second floor
(lv.3) Modified AK-47: Cuba - Battaglia Masonry - there is a room and as you enter it turn left and you will see leader tha leads you underground and just follow the tunnel (thanks to Kazmir)

Magnums:
(lv.1) .357 Magnum:
(lv2) .44 Magnum Force: New York - Carmine Rosato's Compound - in hallway second floor
(lv.3) .501 Magnum Enforcer: Cuba - Battaglia Quarry Chop Shop - if you look at the map there is a lighthouse go there and it's easy to spot

Pistols:
(lv.1) Pistol:
(lv.2) Silenced Pistol: Folrida - Ryan Roth mission - in a mission that he sends you to rescue one of his soldiers there is no way to miss it
(lv.3) Delta M1911 (silenced): Florida - Mangano's Compound - second floor

Rifles:
(lv.1) Sniper Rifle:
(lv.2) Spitzer Centerfire: Florida - Emilio's packing company - is on the roof top, you'll need a engineer to cut the fence
(lv.3) Vintovka SR-98: Cuba - Almeida Compound - is in the second floor on a desk

Shotguns:
(lv.1) Shotgun:
(lv.2) Sawed-off: New York - Corleone's Compound - right side of the main gate behind some bushes, you'll need an arsonist to burn it
(lv.3) Schofield Semi-auto: Florida - Global Storage Chop Shop - on the right side of this little island inside of the small warehouse

lv1的我就不翻译了
lv2：
冲锋枪mp38，在佛罗里达Granados总部的二楼；
.44大口径手枪在纽约Carmine Rosato总部上二楼的路上；
消音手枪在Ryan Roth任务里得到，具体位置我打的时候在一楼屋顶的一个箱子上；
Spitzer Centerfire步枪在佛罗里达Emilio's packing company（地图上可以找到这个名字）的屋顶上，你需要一个工程师来剪断铁丝网；
Sawed-off霰弹枪在纽约Corleone总部（就是你自己家），正门右手边的灌木丛后面，找个小弟用火烧开一条路……
lv3：
AK-47在古巴的Battaglia Masonry，找一件有梯子的屋子（进门左手边），爬梯子下到地下，顺着地道走就行；
.501 Magnum Enforcer在古巴的Battaglia Quarry Chop Shop附近的灯塔里，地图上可以看见那个灯塔；
Delta M1911手枪在佛罗里达Mangano家族总部的二楼；
Vintovka SR-98步枪在古巴Almeida家族总部二楼的一张桌子上；
Schofield Semi-auto（连发霰弹，我的最爱）在佛罗里达的Global Storage Chop Shop所在的小岛，往右走有个小仓库，就在里面