That very blog post describes where they got their materials from, most of it comes from Retromags and out-of-print-archive. You can find downloads over at their sites, and those sites usually also upload to IA.

I don't think you can download directly from VGHF as that is not what it's intended for (it's a research tool)

I'm genuinely asking; why do you want to download the whole archive? What's the purpose?

No. This is by design. I do not like it. It's a tactic often deployed by libraries that want to retain some control over scanned assets. To be fair, normally they are funded by tax payers.

The answer is weaponized scraping.