1000 count pellet cans are the same as the large Kiwi cans. The Kiwi cans were for the gas mask canisters. I saw one set up that started with a leather mask and the riveted on canning jar rings and hot glued in colored plastic panels for the glass. That was for goggles, but the canning jar rings could also be used for the gas mask cannisters. Or build up craft foam and glue and paint in place on a craft foam mask.
I looked on eBay and found various leather masks, some would be easy to steampunk into a gas mask looking with a set of goggles. Look up cosplay costume masks, you will get lots of ideas if you dig deep enough,