Were they prepared in Online TurboTax or the desktop version (CD/download)? If prepared in the desktop version, then you are the only one who could have copies.
If prepared online, log in and go to the section "Your Tax Returns & Documents." Expand that section and choose the appropriate tax year, then the link "Download/print the PDF."
If you log in and find no evidence of your prior returns, or don't find all of them, then you likely have multiple accounts. You can have up to 5 accounts that use the same
email address for notification purposes. A User ID may be an email
address, but it doesn't have to be. It might be only part of an email
address, or it can be anything at all.
NOTE: Before running the account recovery tool below, log out of all Intuit accounts including this user forum, or you might end up in a loop. Then clear your browser Internet cache, close your browser, then reopen it, and go to the link below. You may wish to copy this link so you can paste it into the new browser session.
If still no luck after running that on your phone number and email address(es) that you can access, here's another method.
Go back to the tool again, but this time leave the data field blank, and choose the small blue link that says "Try something else", and it will look you up by SSN and other parameters.