I just made my own from a large flat blade screwdriver. I used a dremel and cutting wheel to notch out the center of the screwdriver blade until it was a proper fit for the slots in the barrel nut, then squared everything up with a small jewlry file. Worked like a charm.
I saw an old post at this link with someone was asking & had the tool.. http://forums.gunbroker.com/topic.asp?TOPIC_ID=434394
There's also a link to a youtube video, Hope this helps..
Search engine is your friend..
Good Luck
Gary/Hk