If you don't know your income, you can always put zero and file the extension.
NOTE: if you end up owing money after all, the interest will start being charged on July 16th until you pay your tax, so go find your forms and file as soon as you can.
Please see this TurboTax FAQ on how to file an extension.
To get your W-2s, try getting the copies form the IRS at Get Transcript. You will want the Wage and Income transcripts from the years ending 12/31/2018 and 12/31/2019.