I got this achievement on my first (current) playthrough of Silent Hill 2 using this guide by GameFaqs user A l e x:
http://www.gamefaqs.com/xbox360/632698-silent-hill-hd-collec...The guide is a little wordy, but following it as best I could I got the achievement when picking up the Ampoule in western part of the Otherworld Rosewater Park, before heading to the Silent Hill Historical Society.
Only item I had trouble finding, and never found, that was listed in this guide was a pack of handgun bullets in Otherworld Silent Hill in front of the Lucky Jade Restaurant, shortly before the guide takes you to the Ampoule I mentioned above. For whatever reason I just couldn't find them and Jame's head wouldn't turn in any direction to point them out. I would have had the achievement one item sooner had it not been for being unable to find those.
Also, if this is your first playthrough, disregard any item in the guide that unlocks the Rebirth ending (White Chrism, Obsidian Goblet, Book of Lost Memories , Book of Crimson Ceremony) -its not possible to find these items on your first playthrough of the game and require a game started from a finished game save to place them in the world. These Items are not necessary for this achievement, though I bet they'd help get the achievement sooner in a playthrough that includes them.
**Credit for the guide and its contents goes to the guide's writer, GameFaqs user A l e x . **