There are 12 missable canisters in all, all in the endgame - on the Balrog airship over the city, and in Meio's Tower. Make sure you have 100%ed all areas of the game before you go into Meio's Tower, as you cannot backtrack after you go into Meio's Tower. Note that you cannot go back to the Balrog airship after you complete that section of the game, either, so keep an eye out when you're there.
The four on the Balrog are all fairly easily acquired - the easiest one to miss is the one immediately after boarding the very large airship; it is down through a crawlspace to the right. The others are mostly "on the way", but keep an eye out for them. There are maps available online.
Meio's Tower contains 4 canisters at the start of the level, before you activate the elevator. The elevator's activation will be obvious; it will appear at the top of the map. Don't get on the elevator until you've collected all 4 canisters.
Two canisters appear on the elevator ascent up to the top; you'll want to collect these as necessary. Be sure to collect them both when you fight the two large enemies on the elevated platforms; after you complete the ascent, you can't go back and retrieve them.
The final two appear immediately after the elevator ascent; destroy them both immediately before going up. The achievement will pop.