TurboTax doesn't store a copy of your W-2. Try asking your employer or their payroll provider for a reissued statement if you need a replacement copy.
If that doesn't work, you can order a copy of your 1978 (or later) W-2 from the Social Security Administration. They're free if you need them for a Social Security-related reason; otherwise it's $86 per W-2. See SSA FAQ 3836 for details.
Wage and income transcripts are available from the IRS free of charge. They're not exactly copies of your W-2, but they contain everything on your W-2 except the state and local information. You can also order a full copy of your return from the IRS for $50, which will include your W-2.