I believe those are co2. You don't want that. You can buy them i believe, but don't quote me on that.
You don't need whip cream cans, you need whip cream chargers. I don't know where to buy those, but I imagine they're not too hard to find since nearly every coffee shop has them.
Goto your local headshop and buy a case, they are called whipit's. You will also have to buy a cracker. If you ask for whipits most likley they will know what your talking about it.
At the head shops in my area if you were to say "whippits" or "cracker" they would get a little flustered and either correct you or ask you to leave. Ask for "whip cream cartridges (or charges)" and a metal "inflator". All the head shops in my area have both of these more or less always in stock and its 18bucks for 24 charges. You also need to get some of those big punching bag balloons from a party store or supermarket (i've used regular balloons but they pop sometimes and also some have this weird powder on them)