Backup file corrupted- How do I recover or locate older backup files?

I synced my original iPhone (with 2.0 software) a few times last night to make sure everything I had on the iPhone was synced to my computer before I restored it, and sold it on ebay. It backed up the iPhone a few times and always wanted to restore it everytime. Well the last time I attempted to sync the iPhone I interrupted the backup process by 'x-ing' out of it during the sync. Now I am trying to get my 3G iPhone synced with the backup of my original iPhone and it is saying that the file is corrupt. Obviously this is because I interrupted the backup process.

So my question is: Is there a way for me to locate an older backup file that may only be an hour older than the corrupt file?
In the preference settings in iTunes I can see the backup files for my phone, but it only lists one, which is the corrupt one. And I searched the finder for recent files, hoping I could find the corrupt file, locate the folder its in and there find older non-corrupt files. Alas, no luck.
I've already restored the original iPhone so the info is gone from that phone. Is there any hope of finding a non-corrupt backup file? Please help.