Birthday Present For My Son?

I was watching this show, Phineas and Ferb, with my two children and saw that the characters had a pet platypus! A crime fighting platypus, too. My kids thought this sounded fun, and I really want to get them a platypus for their birthday. I’ve called all the local pet shops, but can’t find one. Should I just get them a puppy and tape a duck bill and beaver tail to it, or is there a special exotic pet shop I can get one from? Quick replies, please! Timmy’s birthday is in two days.