I've had no luck finding such a thing despite a great deal of looking, and it's easy to see why. The bandwidth for hosting CD images is bad enough, but disk images are just plain enormous, real hard to use, probably the wrong size for your drive, and all that -- who would bother? I had a long-running quest to make a generic USB disk boot image to fill this void until I realized that the computers at work I wanted to make boot drives for couldn't even boot from anything that's not a raw 1.44M floppy disk image. USB boot is a stupid pain.

So it comes down to borrowing a real computer and making your own, or perhaps buying a premade one when available. Sorry.