I realize than most inhalants are dangerous and that nitrous is (mostly) safe. I have no desire to EVER huff dust-off or anything like that. I know Whip cream cans have Nitrous and I have heard that some other aerosol cans do too but I don't know what they are. I also want to know if there are any places that I can buy the Nitrous cannisters not online. I don't have a credit card so I would be thrilled if I could buy Nitrous at Walmart of a different store.
The only aresol cans that i know contain n20 is whip cream cans. You could just go to any grocery store and buy them. Better yet, just go to your local headshop and buy a box of 24 chargers for like 10 bucks and buy a nice cracker and you will set.
Alex is right, just look around at your local headshops. Some grocery stores might have them as well, just ask around. Stores that carry restaurant/bakery/cafe supplies could have them as well though I think most companies just order them wholesale. In the U.S. you have to be 18 to buy them though, just a heads up.