The Silver Needle Case is the fifty-ninth treasure that can be found in Uncharted 2: Among Thieves.
The Silver Needle Case is found in Chapter 17 - Mountaneering. This is an easy treasure to get, though if you miss it, you can't backtrack to get it. Before jumping down the hole towards the corpse with the P08-9mm sitting next to him, simply work your way leftward along the snowy, semi-circular pathway. You'll run into this treasure there, and can grab it and then jump down to claim your firearm.