Since you saved over a file, it may a little tougher for you to get that back.
However, if you recall the names of all the sponsors/websites you need the passwords for, then can't you simply email them all from the email account you registered the account under and retrieve the passwords?
Perhaps you even have some of that information in your inbox already if you have emails from those sites.
The places/sites where your accounts lie will be your best option for password retrieval. Even if you don't remember either your username or your password, odds are you have one specific email address that you would have used when registering, coupled with your name and address.. most good sponsors will be able to retrieve your info from their systems and email you what you need.
It's a lengthy process for sure, but perhaps the time it takes you will ensure that you backup this important data in the future, on computer/disk/paper.. whatever.. but a backup nonetheless so that you don't have to go through these pains again.
