Should be able to get a copy through an App Store link here:
Under step 4 - Get macOS High Sierra
The reason it's reporting as damaged is that a signing cert expired in October(IIRC), so its not trusted anymore. That link should download an updated version that is resigned.
Thanks all for the help. I was not able to get it to download from my 2019 15" Mbp which is really odd. I tried wifi at work, home, and ethernet at both with no difference. I would try and run the command over and over, sometimes it would get up to 84% but most times would just say "Update not found". I wiped a spare 2015 Macbook Pro in the office and it worked first time. Is it because High Sierra is not compatible with my laptop I am thinking?
you need to use the script linked below (as stated above by @wmehilos). Download the script, run it with sudo from the terminal. It will bring up a list of available downloads. 10.13.6 is still on there. It will download it in a DMG (the .app is inside the DMG). I make it a point to download and keep all OS's I can. I do eventually purge.
Curious, did your macbook ever go to sleep during the download? Did you have more than 16 GB free space when you started the process? How much free at the end?
As you can see I was able to download Mojave and High Sierra on my 2017 MBP.
The machine that is downloading it should be irrelevant to this download tool.
It did not go to sleep. I have 105 GB free space which doesn't seem to change when trying to download 10.13.6.
I was able to grab 10.14.6 with no issues. For some reason it just doesn't like that specific one which is just odd.
I did download 10.13.6 with same method from a different machine so I have it saved.
@larry_barrett I use a Mac Pro for my work in the office so it doesn't sleep at all, but even my MacBook is set to not sleep when on power. Free space? IDK, I have 1TB SSds in both so I don't think much about it.
Aso, the script tool doesn't download to Applications. but it shows you the path when you run it.