In Dead Rising 2 for the PS3, Xbox 360, and PC, there are four hidden Zombrex stashes you can get if you don’t want to buy them at the Pawn Shop.
1. Located in Slot Ranch Casino, behind the stage. Climb up on the boxes on the back wall, and jump to the boxes on the right wall and you’ll see it hidden up there on the box closest to the stage.
2. Located in Americana Casino. Go to Bennie Jack’s BBQ Shack and head upstairs to the right. You’ll see some large hanging light fixtures. Climb up onto the bar and jump across the light fixtures to a landing where you’ll see the Zombrex.
3. Located in Yucatan Casino. In the center of the casino you’ll see a pillar type structure. On the south end of the structure you’ll see that you can jump and climb up onto the blueish glowing blocks. Climb up these to the middle section where you’ll see the Zombrex hidden on the left platform.
4. Located in the Underground Tunnels, so you won’t be able to get this one until you’ve unlocked the tunnels. This one is hard to explain, but you’ll essentially need to keep an eye on the map and look for the part of the tunnel that is located directly beneath the northern part of Atlantica Casino. You’ll see a ladder going up to Silver Strip, and the Zombrex is laying on the ground right there.
Here is a video I found that will help if you’re still confused.
