The IRS needs my signature from 10 years ago to prove that the signature she used was not mine… HELP PLEASE!?

My father’s friend needs my help and I’m hoping you guys can help me out too. Well his wife secretly took out a student loan and forged his signature on it 10 years ago, didn’t tell him about it, and recently she died. The IRS told him that he had to pay it, he talked to the Fraud department and they told him if he could provide paperwork from 10 years ago showing his signature for comparison that he may not have to pay it.

However, the problem is he’s moved multiple times since then, has had multiple banks since then, lost most of his old paper work any signature on it, he was told his SS card’s signature can’t be used, and he needs an old signature asap to prove it’s not him before they start going after his wages.

Here’s what I thought of so far…
-Police fines
-Hospital bills
-Taxes?
-Maybe his old bank will still have records?
-Lease or whatever on his house?
-credit card company?
-Utilities bills?

Any ideas will make me VERY thankful, or anything that will pin point it out for me. I’m sure there’s someone he can contact in order to retrieve a signed paper from 10 years ago. If it helps any he gave me his SS# to do searches online and such, but of course I’m not giving anyone that or putting it in any scam sites.

Thanks, and I really really appreciate any answers that are given.

Checks
Deeds
IRS returns
Driver’s license application