Good luck in finding some manuals, eBay and the Nortel site are going to be your best bet.
Having said that, I wouldn't sweat it too much, as it sounds like they already have the system up and running.
If the scripts are well written and remarked, you'll be able to read through them and understand what's happening to the calls.
For everything else, there's this site
On top of that, the site is likely to have the Symposium manuals there, though this is more due to practicality than generousity of the previous admin.
I've got the manuals for a decommssioned Symposium server and they fill one of those office removals box.
Not to mention it's damn heavy too.
Symposium also has a handy little section called Script Commands which also outlines the syntax for the commands.
Personally, I wouldn't sweat it.
If you understand ACD, PABX and MM, you'll pick up Symposium - it's not as hard as some people make out

Hell, I picked it up in less than two weeks, though if you have access to those Nortel courses, they're worth the money.
Good luck !
Good judgement comes from experience,
which usually comes from bad judgement..