Seat Concepts is another option. Looks like a similar shape as a Renazco or XPC (
http://www.xpcracing.com/). They send you the foam and the cover, and you staple it on the your seat pan. The plastic is tough, so an electric or air stapler would make the job easier.
Search KTMtalk or this works as well. I am going to try the stocker, but I have a Renazco on my 640, and I can't imagine anything better, but my money would be on, in order, and coincidentally in ascending order of price but not factored,
1. Seatconcepts
2. XPC
3. Renazco.
Copy/ paste this into google. site:advrider.com enduro engineering seat
http://seatconcepts.art.officelive.com/KTM.aspx