My Orage synchronisation bodge-up didn't reallly work as Orage doesn't remember which archive file it last had between sessions, so here's take 2:
wget -nH -rK your_calendar_file_url -O ~/calendar/google.ics -a ~/calendar/google.log
mv ~/.config/xfce4/orage/orage.ics ~/.config/xfce4/orage/orage.ics.old
mv ~/calendar/google.ics ~/.config/xfce4/orage/orage.ics
Each line is of course a single line of code. Basically what the script does is:
1) uses wget to retrieve the google calendar file and save it in the directory ~/calendar as google.ics. It appends a log of the transaction to ~/calendar/google.log. The directory ~/calendar must exist and you need to create google.log with the touch command.
[If you do not want to append to the log file use -o in place of -a]
2) rename the existing orage.ics file to something else
3) move your downloaded google calendar to orage.ics
This seems to work but there seemed to be a delay on orage reading the ics file. My testing has been fairly minimal so far so it might still be somewhat sub-optimal.
I'll see how it goes.