If you do not have a copy of your 2017 W2, you should first try and contact your Employer to get a copy. If that isn't an option you can order a free transcript online from the IRS by clicking here: Get My Transcript. Your IRS transcript will include your W2 information except for State Withholding. You will need to get that information from your State: State Tax Office Contact Information.
To do your 2017 using TurboTax, you will need to purchase and download the software for 2017 to prepare and mail your return to the IRS.
Here is link to previous years product options: TurboTax Previous Years Products.
Alternatively, you can order by mail or download the 2017 Forms from the IRS Website: https://www.irs.gov/forms-pubs/prior-year.