Bowser Kart is a very rare item, worth one hundred pounds. So it would be quite rare to find it. So, the easiest thing to do is to take your dog on a walk. Make sure it is full, quenched, clean, and has a maximum walk bar. Trace the route around town that covers all ? boxes. And try to grab hidden presents as well, as they hold more valuable items. And, if you have the lucky collar, put that on the dog. Using the lucky collar, your dog will find more valuable items!