Thank you for using justanswer. You would request a copy by filing form Form 4506 (Rev. January 2008)Request for Copy of Tax Return. There is a $39 fee that must be enclosed with your request.
As stated on the form, IRS normally only keeps records for 7 years, but the form also says it keeps some records for a longer period of time, and I think Form 706 is one of them.
You should only have to provide the federal copy, however, if you can't get a copy thru the IRS, then the next place to go would be to the state. Every state has different holding periods when it comes to keeping copies of the tax return, so if for some reason you can't get it from the IRS, then contacting the state your grandmother was living in would be the next step.
I hope this helps
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