Not a fix to your problem but I have also been having a lot of problems with mirrors not found errors. Seems to eventually find a mirror but last night it was bad. Took 10 minutes to start yumex. I am trying hard to get used to yum vs apt and times like that are very frustrating. But most of the time, I can live with it.
My thought, the mirror may be down temporarily.
Fedora 9 (Sulphur) - Gnome
HP DV6910US Laptop
Linux Registered User # 449097