How to develop or get requirements without the user?

I'm working on this school project which is kinda like an Internship but it weighs greatly on a final score, I'm talking this is the last thing I have to do to be able to graduate so I know my software development process.

The problem is our main client. the very fist conversation we had was about how the software was going to be developed and what we should expect from each other.

We had 2 following interviews where we got what epics the system contained and we talked about their processes which they use spreadsheets and we identified a crucial format they used, now it is fair to say he just doesn't seem to trust nobody not even his own employees because he has people verifying the work for other people which results in double the effort, but anyway, the format doesn't contain really sensitive information is just like a summary of everything.

Now this format has almost everything we need to start tackling two of our first defined epics. The problem is that he said he would send us an email but almost a month has passed and we are yet waiting for that format to arrive, he is been busy and he handles a lot of work, but we just didn't get anything done because of that, and it's not just the format that he promised but basic information like what the Mission and Vision of his company are that he said he would give us.

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So my question is: what advice or technique can I use to get developing without the client's input?

I'm not saying I will do the whole system with whatever your advice might be but we can't just afford to waste more time. The whole system isn't that hard to make it's just a managing application for students scores and give information to their parents about how they're doing but the thing is the processes are indeed very unique.