I get the idea that the article (which I already read some years aog, probably because it was mentioned here) just describes the route to the article "Proof of the Umbral Moonshine Conjecture", for which a pre-print appeared on https://arxiv.org/abs/1503.01472

For many mathematical pre-prints can be found at arxiv.org or at the authors website. Searching for the article title with "PDF" usually returns them.

This is why many people who work in research use Sci-Hub, since maller universities often can only afford to pay for the most important journals and not all necessary ones.

Try sci-hub