Help on requesting reports before IEP

So apparently I didn't check the box saying that I wanted the reports before my son's IEP when I signed the assessment plan. Today we had our evaluations and I mentioned I would like copies prior to the IEP. They mentioned I didn't check the box, but knowing this is a right of parents I told them I would send a letter.
My question is where in all the laws does it spell out the rules on this ( how far ahead of time, etc) and is email ok or does it need to be mailed?
Thank you!