I found a perfect hex shaped bowl in a pet store, but it was actually used as a dog treat holder. I asked for a fish bowl just like it, and she dumped the treats out and handed it to me.
I haven't actually measured its water contents, but it is much heavier than my one gallon, so I'd guess it holds around 2 - 2 1/2 gallons. Anyway, it's plastic but beautiful looking and a little lid with holes for air fits perfectly over the top hole. I'd like to get another one though, and I was wondering if anyone knows where I can find one for my other betta.--(perhaps a restuarant supply shop?) I can't find petstores that carry them.