I just replaced the seat cover on my KZ 650B which was totally trashed - I went on line and found this site:
http://www.motorcycleseatcovers.com/
It arrived yesterday and by following the instructions carefully now have a very nice replacement cover installed - it arrived promptly and the finished result is excellent - obviously if the foam is no good on your seat then no replacement cover will help you - total cost to me was $72.00 which compared to a complete new seat or even a half way sensible used one was pretty good in my opnion.
Lee