Where can you buy Dungeons and Dragons?

The best place to look for D& materials would be your local game shop. Not like GameStop or ones that sell primarily video games, but the shops that specialize in card and tabletop games. These same shops often sell comics as well. You may also find D&D books and boxes at book stores, and stores that sell used games/cds/dvds/books, like V-Stock or Slacker's (if you have those in your region). If all else fails, online shopping on places like Amazon will always get you what you need. Support your local game shop before shopping online!