Find an unlimited Usenet provider that works with your budget and location. Plenty of debate out there on which are best, and if you need a second pay-per-GB provider for filling in missing parts or not.
Spin up SABnzbd+ or a similar Usenet client on a local PC/NAS/etc.
the hard part - find a quality private Usenet indexer site that you can get an invite or has open registration.
Download the nzb files for the Linux ISO that you want from your indexer and open it with your Usenet client. (There are ways to feed the nzb file directly to your client, but that’s for next lesson).
Client looks for all of the parts listed in the nzb file on your Usenet provider, then downloads and unpacks them.
Et Voila - Linux ISO appears in your downloads directory.
A VPN is probably unnecessary, as most Usenet providers don’t log who downloads which files. Also, you can often hit your ISP’s max download rate from your Usenet provider, and there is no “seeding” to worry about.