They are a little hard to find - not everyone has them. I found mine at the little souvenier stand outside the Autopia entrance near the bathrooms. I have also seem them at WOD. Last time I looked in Emporium for them they told me they kept running out and only had the animals.
The Emporium on Main Street is a good place to look but like the previous poster mentioned, they often sell out of some of them. I bought a few at the Emporium and then had to go over to the souvenir place between Autopia and Innoventions to get the rest. Good luck!
Actually only a very small handful of stores in the park carry them and they run out all the time. Since these are relatively new, hopefully they will get the message and start offering them more places and keep them in stock.
Emporium and the Autopia shop carry them as well as a store in Toontown according to a PP, but I have never seen them anywhere else in the park. When I wanted to buy mine, I looked everywhere and asked every CM in every store I checked in, and they kept directing me to same 2 places, Emporium (which was sold out) and WOD (which was also out). I ended up buying them by Autopia, and I only found them there by chance because I had to use the adjacent restroom.
If you wanted to get them by mail, though, there are a few options. I am not sure if Delivears can send them out, but I don't see why not, Mouseshoppe.com has them as well as Laughingplacestore.com, and you can always find them on Ebay of course. They cost $3 in the parks and we have a 7.75% sales tax too.