Have you already checked the M&A cases available on Preplounge? If you haven’t yet you will find them under ‘Resources’, ’Case Library’ and then filter the Topic ‘Mergers & Acquisition’.
Also, you might want to check the bootcamp lesson on M&A here:
Other than that, I have been using two M&A cases based on real projects to interview candidates during the years but I don't have their solutions in a written format.
Hope it helps,