The Tibetan Flint Lighter is the sixty-third treasure that can be found in Uncharted 2: Among Thieves.
The Tibetan Flint Lighter is found in Chapter 18 - Heart of Ice. located directly after you obtain the Oil Lamp (while swinging from the rope). This hard-to-spot but easy-to-acquire treasure hangs off of the side of the flat gear (This is the gear AFTER you land and fall and ride that gear down). Hang off the side of the gear and the bottom and ride it round and under the rocks. Grab the treasure just as you emerge from the other side.