There is no way of getting a registration code for your Sims 3 game from anyone over the Internet. Even if a person did give you their code you wouldn't be able to use it because each code is unique and cannot be applied to any other disk other than the one that it came with. If your friend has a disk that they are not using then you could ask them if you could borrow or buy it off them because you are able to use the same disk and code twice. However, you cannot interchange codes between disks.
If they can help you then it will probably take a couple of emails between the two of you to sort out the problem as they will probably ask you for some information about your disk.
Get in touch with the person you bought it off to see if there is a simple explanation why you haven't got the user manual. If there is a simple explanation then they will probably be able to sort something out, even if it is just emailing you the registration code.
- Contact Electronic Arts.
If they can help you then it will probably take a couple of emails between the two of you to sort out the problem as they will probably ask you for some information about your disk.
- Bought off the Internet.
Get in touch with the person you bought it off to see if there is a simple explanation why you haven't got the user manual. If there is a simple explanation then they will probably be able to sort something out, even if it is just emailing you the registration code.