you can do it by using a cheat but im not the one who will tell you the cheat. just search gta the ballad of gay tony cheats then it may show you.
There is one you can buy in the back on Andreas' gun car. There is also a cheat.
u call 1 of they guys on you phone they should have gun van on them then call them if they say there on there way an a should appear then just go towards the a there will be a gun van u press lb if u...
by pressing r1 or lt in xbox 360 also its in your weapon inventory
With the "Episodes from Liberty City" game which has TBoGT. You dont need GTA4 if you have this.