I use this utility to download my installers:
https://github.com/munki/macadmin-scripts/blob/master/installinstallmacos.py
You can download all the current installers (including any current beta). it will create a DMG file. Just open the DMG and copy the installer from the Applications folder. You can then create a USB installer by using the createinstallmedia command.
I've tried to copy and paste the installinstallmacos.py content in TextEdit and save as a .py file, but even after opening the file in EditRocket and verifying it via debug, whenever I try to launch the python executable I get a syntax error. Could someone please tell me what I'm doing wrong or upload the installinstallmacos.py file? If I right-click the file on the GitHub page and "save as" the downloaded file has an .html extension...
Cheers