Where can I buy the series in manga form?
Your best bet is at an anime convention, especially if you’re looking for the original 42 volumes. Ebay is another place where you may get lucky, sometimes people are clearing out there attics and sell a lot of there DragonBall merchandise. However, you may not find all 42 at one time, you’ll probably have to purchase all of them from different sellers. If you’re looking for the kanzenban, then my best suggestion would be Amazon Japan. Knowing Japanese is really useful for this site, but it’s not absolutely necessary. They offer certain pages in English, but before buying you must first set up an account (remember, you can’t use your U.S. Amazon account). If you decide against this route, then some good English sites would be Kikiwai and the Sasuga Japanese Bookstore.