Go to the map "Shi no Numa" and get enough points to open the doors.

Buy the perk cola's and the random box, (note this ONLY works in Flogen (the front area with the big gate) and the Storage area and you must have at least 4000 points for the box and cola).

First you buy the box, then run over to the cola machine, wait until the gun is loaded then buy the cola.

Then as fast as you can run over to the random box WHILE STILL DRINKING THE COLA and buy your gun and voila!

You now have 3 guns at your disposal.