Can I file a prior year return for 2017 if the businesses I need a W2 from are no longer operating?

Yes. If you are unable to get a W-2 from the employer, you can get a copy from the IRS for a fee (assuming the employer issued one)**.

There is a procedure for for creating a substitute W-2. TurboTax can handle this. A year end pay stub will usually suffice for getting the info needed.

** You can get a free transcript from the IRS, which will probably have all the info you need. See https://www.irs.gov/taxtopics/tc159

Is it for self employment income?  You don't get a W2 for that.  You get a 1099Misc or just report it as cash.  Did they take taxes out if your payments?