NOTE: I did not come up with this method on my own. It was found on 360achievements.org. I take no credit other than spreading it to you guys.
This was done on normal difficulty and the room that replenishes the items requires a power node for access(has been confirmed to be doable on easy also)
The Save Station that is located on Chapter 14 after the anti-gravity section. Shortly after sticking your eye with needle, you'll be chased by the necromorph that doesn't die. You'll eventually reach the anti-gravity section. After you pass the anti gravity section, you go through two doors and on your right will be a door requiring a power node for access. This is room that replenishing the items. You'll find the Save Station two more doors if you head left from that T intersection.
Steps (read description above to locate starting point):
1. Unlock the door with a power node. Title above door: 6: Secure Storage, Power Node Access Only
2. Advance through two more doors to reach a Store, Bench, and Save Station.
3. Save at Save Station after the anti-gravity section on Chapter 14.
4. Reload the save point by quitting to main menu
5. Back track to the anti-gravity area (most of time you can go directly to the room). Once you get back to the anti-gravity area, go back through the last two doors and go into the room on your right. This is the room that required a power node to open. Inside this room is where I find either 2 power nodes, 1 ruby semiconductor, and/or 3k credit.
6. Go back to Save Station and save the game.
7. Repeat steps 4-6
NOTE: if you start finding only credits in the room, try going all the way back to the switch in the antigravity area, then go to the room. Doing this has reset the 2 power nodes for me.
(Also have read that you can also restart checkpoint instead of loading from a save on main menu, but unsure.)
Darn, I'm pretty past this part. Would've been nice to know so I can grab some weapon achievements faster and go straight to Hardcore. Oh well, guess I'm doing Zealot first, then Hardcore. Wonder when they'll patch this.