You are going to find it difficult to located a fastpitch bat heavier tha 26 oz. Manufacturers make fastpitch bats with lighter weights to help younger female batters increase bat speed. For years it was unthinkable that any female player should swing a bat more than 23 oz, even at the upper levels (18 and older). What we are seeing now is the use of the heavier bats 26 oz in the college game.
Speaking ASA there is no requirement to use a fastpitch bat in a fastpitch game. The only requirement is that it must be a softball bat that is not on the banned list. So, you can find numerous softball bats that have the weight range that you want.
Try
www.softballsales.com or other web outlets as they have the best prices and complete selelction.