Tried to install High Sierra but failed. I think Apple shutdown the installer server already https://files.mastodon.social/media_attachments/files/111/061/691/251/896/891/original/c1f387bc7fa23527.jpeg
@b30368b8 is it hiding in the Applications folder on your HD? I downloaded it for a reinstall a few weeks ago. I moved it to a bootable USB drive and stored it away after the install. I did the same for Mojave. Look around. Someone probably has a ditect link to the OS on an install server. Thats how I found both OS.