I have designed this in CAD in the past.
I did not make the spider part was intending to use it for a very similar purpose. I followed the ISIS white paper to the best of my ability and I believe that I did it correctly but have never CNC'd a component from the design. So there fore I can not confirm that it is true.
The reason that I decided to design from scratch is because all the CAD drawings/free files I could find on the web (ex. Grabcad etc..) did not actually adhere to the design specifications according to my evaluation. And I didn't want to risk CNC one off prototype a paperweight in the end....
From memory, CNC a custom part like this would run a couple hundred $
The white paper
http://www.isisdrive.com/isisdrive/ISIS ... t_revD.pdf
here is a pic where I incorporated a 6 hole disc/cog spider