Load and Performance tests with >1K users for Graph API based mail application.

Question

Hi,

I want to do load and performance testing of our Graph API based email application.
Recently we started to encounter errors for customers with a large amount of users.
Our dev tenant with 25 licenses from the Microsoft Developer program has served us well, but we want to test cases with >1K users.
We have done mock tests with simulated Graph responses, but we want to test with actual responses.
Is there a method that will allow us to do this without needing to purchase thousands of licenses?

Thanks