There are lots of small shops scattered throughout the mall, but the main draw there is Mandarake (mandarake.co.jp). There are something like 20 different Mandarake shops in Broadway, each for a different specialty. They are a secondhand store, however, so you may pay a premium for older items regardless of condition. They have most of their inventory online, too, so you can still window shop if you can't visit in person... plus, they ship overseas.
If you happen to be in Tokyo and are looking for other places to buy figures, Akihabara has a large Mandarake and numerous shops throughout the neighborhood, such as Jungle and Liberty.