Since you have not filed any tax returns there is no copies of tax returns to receive.
You can get a Verification of Non-filing Letter from the IRS using the IRS transcript website - https://www.irs.gov/individuals/get-transcript
No one keeps returns older than 7 years so you are out of luck. The SS administration will have your work history ... log in and get it here : https://www.ssa.gov/myaccount/?gclid=CjwKCAiAqJn9BRB0EiwAJ1SztZJNkMGthQ819EHV0Z6Q9xNb2KAqgI39jRiwllBJxjrbgIoq7tO98hoCdNAQAvD_BwE
File a non filer return by 11/21 here only : https://www.irs.gov/coronavirus/non-filers-enter-payment-info-here
if you worked for a corporation of any fair size, your pension checks will start flowing to you when you reach the age of eligibility.
If it is a smaller company, you'll have to tell them your pension payment does not require a tax return from you.
Get an attorney and have the attorney write a letter to your company.
If you worked long enough at a company to be vested in the retirement plan, then getting your pension should simply be based on reaching retirement age---not providing them with tax returns. Are you sure they really asked for that? It sounds like there might be some sort of misunderstanding. Or else we are missing some information.
@Mazurkiewiczdick In your other thread you mentioned that you have been receiving Social Security. If your ONLY income during these past years since you left the employer has been Social Security then you were not required to file a tax return.
Your other thread: