So I got a bit bored and decided to make this: (Also: Keep in mind that not all guns are listed, just most of them)
The text in bold represents the name of the location which can be found on your map.
Gun Upgrades:
-AP0
-SMGPK
-Morano Thompson
-BAG
-M1911
-Kar98k
-Mk23
-Glock18
-MP40
-Steyr AUG
-Lexel Rifle
-Peace Maker
Lock N Load Gun Shop
-HoneyBadger
-AssaultShotgun
-PP90M1
-G36 Tactical
-Auto Pistol
-G36 SV
Maccus Gun Shop
-PKP Osiris
-Uzi Maccus
-PL9 Shotgun
-WH42
-SA80
-G36K
-GT SIG 516
-M416
187 Guns
-Socom
-FNP90
-G_F2000
-SMR
-L96A1 Sniper
-Raffica
-KMP9
-TAR21
-DSR50 Sniper
-Ghost M4
-FIM 92 Stinger
-Paintball Gun
-Jack Hammer
-AF2011
-F2000 Tac
-MG36
-Spectre
Ozzy's Repair Shop
-Souizen
-FMG9
-Tachi Scorpion
Gun Point Shop
-M3
-M16
-Tec 9
-Luger
-Shipka
-BAR
Panther International
-PBP Shotgun
-Tec 9
-Shipka
-Sten
-MP7
-Raffica
Chrisz's Gun Shop
-Starter Gun
-Uzi
-Shotgun
-Handgun
-AK47
-Colt 6
Ammo Mart Shop
-ACR
-Steam Punk Pistol
-M1 Carbine
-Blunderbuss
-Skull Cannon
-Bone Thrower
Fort Knox Bomb Shop
-Gold Uzi
-Famas
-M4
-Artillery Cannon
-Souizen
-Pink M4
-Metal Storm
-Golden M4
-SS50-A3
-Rafor
-Assault Rifle
-WH64
-Five Seven
-HK416
-M249
-M60
-Ghost Ripper
-Gold Souizen
-MTARX Tac
-Gold Desert Eagle
-MP9
-Golden Sten
Mephace Gun Shop
-AB8
-KAP40
-Auto Rifle
-Sawed Shotgun
-Sawed AK47
-M8A1
-K180
-SnowBall Cannon
-Steet Rifle
-Gas Launcher
Aimpoint (On-Land)
-44 Magnum
-M1911Tac
-Skorpian EVO
-Vulcan Minigun
-FMG9
-SVD
-Fal OSW
-PDW SD
-AA12
-Bushmaster ACR
-M107
-MP7
-MK14 EBR
-RPG 7
-ARX160
-MPX
-SCAR-H
-A-91
-Spas-12
Aimpoint (Island)
-P99
-MK12 SPR
-Lapua 338
-M16a3 M203
-Model 1887
-AKM
House 26 (You'll need a key to enter)
-AP7
-Taurus
-Neo Rifle
-P90
-Desert Eagle
-Gold Desert Eagle
Candy Factory
-Candy Bazooka
-Gummy Gun
-Facebook Gun
Gangster Store (Located in mall)
-870 Field Shotgun
-Greaser
-SKS
-Makarov
Repair Shop
-Chili Pistol
-Graalians Bow
-Kar98k
-Lucky Rifle
-M1911
-Regurgetator
-Bunny Rifle
-Chili Gun
-Cinco Cannon
-Hollow Chain Gun
-Egg Launcher
-Facebook Gun
-Blood Moon Wand
-H-Cannon
-Skull Cannon
-Skull Gun
-Bone Thrower
-Present Launcher
-XMA-13
-Blunderbluss
-Taco Cannon
-Heart Breaker
-Cupid's Bow
-Steet Rifle
-SnowBall Cannon
-Spooky Bow
Underground Exotic Base
-Darkmatter Cannon
-Vampiric Staff
-Carnage
-Inferno
-X75 Assault Armor