I've heard that there is a secret mask shop in the lagoon area of the Water Reservoir, the same area where you can find the gas mask. Is it actually in the game and, if so, can you give any hints on where/how to find it on purpose?
I believe I saw that there was a very rare, random chance for it to appear, so I've been trying to respawn in that area via walking into random buildings or using the transryte crystal.