I wrote a brief guide to getting the courier to spawn, it's available on the wiki here:
http://wiki.project1999.com/A_sarnak_courier
If you want an in person demonstration I would be more than happy to help out, just send me a tell if you see me online. If you're doing this on your druid, I think your best bet would be to charm a barracuda to do most of the killing of the 30 second respawns after you AoE down all the potential placeholders.
As for the droprate, I was averaging one ring every 2-3 hours when I was farming them. I haven't farmed them in a long time, however, and the drop rate may have changed!