itch.io

It appears that there are four .wad files all the assets of the new episode.  (id1.wad, id1-res.wad, id1-weap.wad, and id24res.wad.)  They do include a .txt that claims they work with other engines, assuming they have the proper support (MBF21 and ID24 as listed in the .txt).  Though no idea if they actually work properly.

Thank you SidAlpha for pointing me to this very fun game.  I'll have to take a look at your other works.

No, it's not an official episode pack.  That's why it was sold as a book with a free disk.  And that's why it's not included.