And just for safety: those things should prevent you from breathing in smoke. They have a filter in that mask and are far more effective than a wet handkerchief.
Thrift shops and designer stores are both my bet. Those where already high Fashion in the past if you ask me.
Edit: Maybe in Shops where you buy extras for your suits. Looks to me like either a (oversized) jacket for when you are not wearing a suit or a jacket for above the suit.
To every rule there is an exception