The canned air can get from Ace hardware.  There's 2 brands available locally.  Ace brand n Ambersil. Ace is rm20, Ambersil is rm40. I prefer Ambersil as it's twice the size of the Ace, also a lot more air pressure to clean better.
How long it lasts? Loooong time unless u got like Incredible Hulk fingers that simply press the trigger.