Whatman 1004-050 Filter Circles, 50mm Dia, Grade 4, 100/pk (PN:1004-050)
 
Suggestions:
Use a sheet of this paper to absorb odor passively ("odor soak"). These training aids can then be hidden, left behind, or cut into 1/2, 1/4 and 1/8 pieces.
Put a sheet of Whatman Paper on the top of my membrane holder while my TADD is closed and not in use. Then, when I go to train, I have two training aids, the TADD and an odor soak paper that I can use in another scenario.