Mushroom growing-cakes!

Yo. I was looking around a few sites that sell spores for mushrooms, and I noticed that the ones that sell growkits don't ship to the USA, understandably.

Does anyone know of any sites that sell pre-sterilized cakes for growing? I've seen a few, but none which have cakes that are good for growing psilocybin. Would any cake work, such as a wood or straw-based one? Those are all I could find :\

Does anyone have any experience with pre-sterilized cakes bought on the net?

Also, on the City's shop, there are shipping restrictions on every page of the growboxes, however not on the fresh psilocybin mushrooms themselves. I'm guessing not, but does this mean that the city will ship them to the usa?