So I'm out of luck upgrading?
Well, after making the modifications to your F10 repo files as I suggested (I got confused and thought you were at F12 currently, but just re-read your post and see you're on F10), you will still probably have the problem of the upgrade not finding the F12 repositories for the same reason F10 couldn't find it's own repos. Is your goal to upgrade all the way to F17, the current latest version? I would strongly recommend backing up your important data first though, before trying any type of upgrade. It's your responsibility to safe guard your data.
I can still see 13 and 14.
I'm not sure what you mean here. Perhaps you mean you can still access the F13 and F14 repos from machines running those versions of Fedora. Yes, there could be some working mirror sites for those still lingering around. Switching to Centos6.0 (I think that's the latest version) would be even better. It has a much longer support life cycle than Fedora. Trying to upgrade your way from F10 > F17 is just fraught with so many ways to fail along the way. And besides, I thought using "preupgrade" automatically tries to take you to the latest Fedora version. But maybe I'm wrong about that, as I've never used preupgrade.
There is also the "yum" method of upgrading, but that too might fall victim to the repositories being moved to the archives. For example, going from F10 > F12:
# yum --releasver=12 update
Might work, or maybe not. Note, "--releasver" may not be the exact option syntax, I'm in W7 at the moment and can't verify.
I still say, backup your data, and do a clean install. Anything else is at your own peril. Well, for that matter, anything you do is at your own peril.