lil_itchibut Did you ever install Sims 3 on a computer you have access to now? If you did, and you haven't done a clean uninstall of the game in the interim (or otherwise wiped your computer), you can find the CD keys in the registry. Click Windows key-R, enter regedit in the run box, and expand this path:
HKEY_LOCAL_MACHINE\SOFTWARE\WOW6432Node\Electronic Arts\Sims(Steam)
The base game and each pack you own will have a folder in this category, and if you expand it, you'll see an ergc folder underneath that. Click the ergc folder and you'll see your CD key for that content.
If you can't find the keys there, I'm not sure what else you can do other than work with Steam to recover the account another way. It should be possible to provide bank statements or something like that, but I've never had to deal with Steam support on this subject.