There really isn't anything for the small sport boats. To be perfectly honest... the stock grate works very well.
One thing to remember... if you put a grate on that has smaller openings... a few things happen.
1) You can restrict the water inflow, and that can lead to cavitation, or reduced top speeds.
2) It will plug up easier. The pump can easily chew up seaweed, or lake grass. BUT... if you put a restrictive grate on... it will just plug up, and you will have to go for a swim to clear it out.