I need help finding a certain weapon.

Hope this helps: link

I can help! Keep in mind that you need to make alot of progress in the game before you acess to them! They only show up after you use them in a mission! I forget wich one! Anyway the easiest one's to find is in Mad dogg mansion por the cozinha on the first floor! Thier under the stairs that leads to the large hallway with several rooms!