Answer:
you cant buy a bubble blower, it is just a feature that the kids come with.
There IS a bubble blower that sims can purchase. I believe it comes with University. It's a fairly large item, looks quite colorful,and the sims will get, literally, high - floating off the ground.
dont listen to the first one. There is a bubble blower that comes with the sims 2 University. If you do motherlode, you will get lots of money and by as many bubble blowers as you want :)