You may have to wait a bit before somebody comes home from riding, reads the forum and then remembers they have one hanging on a nail in their garage. (-;
As an alternative:
You might turn something up on eBay, locally with Craigslist or if you don't mind such places AliExpress.
Be aware that unless you are into modifications the seat has to be specifically for the 1998 to 2003, 750 ACE or if sourcing from Asia the 1997 to 2003, 750 or 400 ACE.
There are usually a fair number of offerings out there including simple knock-off replacement covers if your seat foam is still good.
You might also consider visiting an auto or marine upholstery shop to see what they can do to fix what you have.
There are several custom motorcycle seat rebuilders out there, sorry I can't think of their names, but Google should turn them up.
There is some good info referenced in this post.
No idea about the Mustang "stretch-over" covers, I'd be afraid of it shifting around over time, but maybe not, I have been happy with the quality of the 18 year old Mustang 2 piece wide touring seats on my bike, so I know they make good stuff.