The next page is “Getting started” (http://www.conmicro.com/hercos360/getstarted.html). It says:

“The best source is the CBT CD-ROM, which contains Rick Fochtman's OS/360 distribution. This has not only the OS/360 distribution files, but also the source to the operating system and utilities, as well as some useful documentation. There are many, many other useful files and utilities on the disk, and it's a must for anyone wanting to experiment with OS/360, as well as any systems programmer on a modern OS/390 or z/OS system. Ordering information is at the CBT Tape site.”

That CBT Tape site is a sight to behold even if you have no plans to run OS/360: https://www.cbttape.org/. Bonus link: https://www.cbttape.org/funny/bug3.jpg