In the Shop:Edit
Fangtooth Respirators may be puchased in the shop in amounts of 1000 for 30 Rubies each.
In the Wilderness:Edit
They can be found in amounts of 100 and 500 in the wilderness when Lakes level 7+ are conquered. Chances of acquiring them are slim, but to increase your chances of recieving them from a battle, try conquering Lakes at level 9 or 10. *
Fangtooth Respirators can be recieved as a drop from level 7+ Anthropus camps in drops of either 100 or 500, but as per above, chances of acquiring are slim. to increase your chances of getting them, conquer camps above level 7, or attack numerous camps at once.*