Even if you could find the 2018 TurboTax software somewhere, it will not be the final version, but you will not be able to get updates and you will not be able to get state programs, so the software will not be usable. So the answer to your question is no, you cannot use TurboTax to file for 2018.
Some other tax software companies might still have 2018 software available. A local tax professional also might prepare a 2018 tax return for you.
It's too late to get a refund for 2018. You can file the tax return, but if it shows a refund you will not get the refund. If it shows a payment due, you still have to pay the tax you owe, plus penalties and interest for late filing and late payment.
A 2018 tax return can no longer be e-filed. No matter how you prepare it, it will have to be filed by mail.
