You can Buy them Online or at Anime conventions.. the anime Convention i wen to i got a Miku Hatsune Plush
Ebay
In Five Nights at Freddy's 2, plushies can be obtained by completing the minigames throughout the game. Each minigame has specific conditions for acquiring plushies. Make sure to explore the game thoroughly and interact with all elements to increase your chances of finding plushies.
You can buy it at Amazon.
You must buy their voicebanks.
toys r us
look on a online shopping site
You cannot buy VOCALOID figurens in the U.S. unless you go to an anime convention or buy them online from Figma or Nendroid.
South Park plushies are very rare. The only place i have seen them for sale is the Tobacco Station. Otherwise just try claw machines.
You can buy some at the Japan section of Epcot in America. Some are usually for sale at Pokemon World card tournaments. If you can't find any at any of these places, go on Ebay (there's always plushies on Ebay!).
From the internet (I don't suggest this) or buy it in Japan
You have to buy it to have an activation number.
If you're talking about the Japanese vocaloid then you can't. But there are several ways to change vocaloid into English once you have it. Like in this video for example: http://www.youtube.com/watch?v=D01vaheD-Oc