The late 80s were dominated by the "Slaves to Darkness" and "The Lost and the Damned" supplements. Issue 110 provided additional Mutations tables and Chaos warband rules that remain legendary for their sheer randomness and creativity.
Games Workshop, like many publishers, has historically been protective of its intellectual properties. This means that back issues, while sometimes available in scanned form, are often not officially released in digital formats due to copyright and licensing concerns.
Here is the frustration. Despite the internet being flooded with modern 40k leaks, finding a clean, complete, is notoriously difficult.