I lost my registration code help please!

For your Sims 3 games:

If you purchased the games from Origin, then they were automatically registered for you.  You should be able to download the Origin client and download your purchases from the "My Games" tab.  You would not need the discs as these would digitial downloads.  

If you never registered the games and bought them elsewhere, then you need the serial code to register the games.  Serial codes are on the game manual inside the case or in your email if you purchased any of them as digital downloads. You can don't have those things but have access to a computer where the game were originally installed and are still there, you can find the serial codes yourself: http://answers.ea.com/t5/The-Sims-3/FAQ-Lost-and-broken-DVDs-and-missing-serial-codes-What-to-do/td-p/14230.

Sims 2 games: 

I don't know much about the process for these or if it's the same or what, but I did find these posts on the topic.  Check out that board for more info: 

--http://answers.ea.com/t5/The-Sims-2/Information-How-to-register-your-Sims-2-game-in-Origin/m-p/368020#U368020

--http://answers.ea.com/t5/The-Sims-2/Information-Obtaining-a-Replacement-Registration-Code/m-p/367978#U367978

Hope this helps.