Pet bird clubs are often a good way to find local breedeers. Try googling for "pet bird club Massachusetts" and any other state that you're interested in. After you've found several bird clubs, contact them to see if they know any cockatiel breeders in the area.
You can also do the same thing searching for "cockatiel breeder" instead of "pet bird club". Also check out craigslist and ebayclassifieds.com