Good point, if you insist on wearing a gas mask in your lab, it would be in your best interest, to get a brand new cartridge that is designed specifically to protect you from substances in question. The problem might be finding a commercial cartridge, cannister, what have you, that will fit your military issue mask. I am not sure how universal these cartridges are. I would guess the military had these specially designed for themselves, and there is probably no way in hell you will be able to find a cartridge to fit what you have. I could be wrong, but If you really want to wear a gas mask you should buy a commercial one that you know will accept the cartridges that you need. Some info below about NIOSH requirements.
Concentration of H2S
Minimum Respirator Required
Up to 100 ppm
Half-mask respirator with approved cartridges. Willson® 1200 series or 5000 series ValuAir® with R25, R26, or R35 cartridges. Willson ValuAir Plus, Premier and Premier Plus with T05, T06, T08, T05P100, T06P100 or T08P100 cartridges. Willson Freedom® 2000 series models 2X05, 2X06, 2X08, 2X18P100. Willson MX/PFÔ with C30A or C30P100 cartridges.
Up to 300 ppm
Full-facepiece respirator with approved cartridges. Willson model 1600/1700 with R25, R26 or R35 cartridges. Willson 6400/6500 series with T05, T06, T08, T05P100, T06P100 or T08P100 cartridges. Willson F710 with C30A or C30P100 cartridges.
Above 300 ppm or unknown
Gas mask with approved canister. Willson model 6600/6700 series with 65 canister. (Acid gas approval on the 65 canister covers hydrogen sulfide. Canisters do not require specific approvals as cartridges do.)
I think you can get these masks with tinted face shields also, which will hide your identity when someone breaks down your door to see what you are doing in an apartment wearing a gas mask. Sorry I can't get this image out of my head. LOL..