Hopefully, you may have deposited the check into your bank account. The bank would have scanned the deposit and it remains in the records. You may actually have access to it via internet.

Otherwise, you need to contact the administrator of the plan. I don't know of any, although there may be some, companies that administer its own 401K plans. There is usually a separate entity. Look for old statements and contact the financial administrator.

Even if your company went out of business, the people who handled your 401k are likely still in business and can help you.

If all you want is a check and you've cashed that check, your bank will have a record of it and will be able to supply it for you. If you want to discuss your 401k beyond that, the name of the company that issued you the money would be listed on that check, most likely with a contact phone number.