It used to come on DVD's, now you can create one from within mac os
I used to use CCC (Carbon Copy Cloner) to make a mirror, but it doesn't like to boot from the mirror (it does, but I can't use any of the secure stuff). Also CCC destabilizes my system. If I have it running all the time, I crash -a lot-. Since I yanked it, I haven't had a hard system crash in months.
These days, I just make sure the Time Machine backups keep going, and I'll use CCC on a one-shot basis to make occasional disk clones (makes for a much faster restore).
Maybe I misunderstood you, but you can make a bootable USB stick from the installer app:
It's been a while, since that was possible.
The M-series just basically put a fork in it.
That, and CCC kept crashing the machine.