Hobie sells them they are called side kicks, they actually work well and are not too expensive. They are kind of for sailing with the Hobie sail kit. You may not know this but every Hobie kayak is designed from the ground up as a great sailing boat, you only need to add the Hobie sail kit, (all Hobie Mirage kayaks use the same Hobie sail kit).
We had an Oasis and installed a weighted keel that works similar to outriggers (making the boat completely un-tippable). We used it when sailing our Oasis mostly. We live right by the ocean and mostly go in salt water where there is often surf and waves.
The simplest weighted keel solution is a 2 ft section of 2" dia PVC pipe filled with lead shot, then caps put on the ends. You then tie the keel weight under the boat with spectra string (Hobie kayak grey rudder line) hanging down about a foot below the boat suspended by the 4 corners. When you ground the boat, the keel weight just slips out of the way (doesn't hurt a thing). The PVC tube doesn't slow the boat down much at all because there is very little drag (like a torpedo), however the spectra lines act like magnets collecting up any seaweed or sea grass that you go by. I think it works out a 2" dia PVC tube 24 inches long works out to exactly 25 lbs, the tube is filled with lead shot (we just cut open and emptied a bunch of 2, 3, and 4 lb weight belt bags, and poured them into the tube).
Hope this helps