Well if you mean like buying them on your game, I can help you. Go out and tap Kennel, and you can buy a dog or look at a dog. They cost money, too. You can get money from contests if you need it. I lost my Nintendogs game, so if this doesn't make sense, it's because I haven't played Nintendogs in forever!
Go to walking your dog and then go to the big yard that has post set up in the picture.
it doesn't take alot time, but It takes about 2days. I am sure.
I believe you get it while you're walking. You can look up at the map to see if the little doggy marker stops, if it does hurry up and look at the bottom screen of your DS. There might either be a present or some garbage. If it's a present, hurry up and pull your dog back so it'll see it and give it to you. if its garbage pull your dog forward so it doesn't get sick and eat it. There's probably a 1 in 30 chance you'll get the Mario Cart or the Helicopter. GOOD LUCK!