I have been looking around for the same thing. I bid on a pair of Otari Reel Adjusting Discs on ebay,
they went for $20. WTF. I found a guy who designed some on an autocad, but didn't put up a template.
From suggestions i have read I think cutting them out of the tops of Margarine tubs, or using the clear plastic
flexible sleeves for Cd's you can buy for 5c each seems best.
So I knocked up a template quick in illustrator to print out. I just made a .5" hole in the center to make it easier to cut out with a blade.
Here is a basic PDF template you can print out and cut out. It is 4" wide, with a 0.5" hole.
http://www.sendspace.com/pro/dl/nfps00Also the Teac TZ 612's have built in adjusting disks. i have a pair and they work fine on my Otari mx 55 and 5050.
