I'm trying to find REALLY REALLY big round "fish" bowl that would be a centerpiece for a wedding?

Okay. Your link doensn't work but if you are located in the New England area then try CHRISTMAS TREE SHOPS - they are located mostly in Machusetts. They have a great collection of gl (including large fish bowls) for centerpieces. If thats not possible try a Michaels, Joanne Fabbric, AC Morre, or any craft store!!!!