if possible, try placing it horizontally in the tank, with the output facing up... i've done this before, might give you what you're looking for?
other then that, you may want to look into getting a differnet filter, i have even seen some that will move back and forth on their own, but these are quite expensive. or mabe one that creates a wave like motion
as far as i know, there are no parts you can buy for a fluval, other then what already comes with it