Sometimes they sell Beanie Babies at Shaws Supermarket or Hannaford. I don't know where you're located but if you aren't near any of those stores then you should try ebay or like elyse249 said craigslist.
some gift stores might sell them, otherwise if they dont (and there not being made anymore or are retired ones) youll need to buy them new-secondhand on places like ebay
craigslist? lol you can find anything on there