I found some 1/16" and 1/8" cork rubber on amazon.  The 1/16 seems to be about right and is much more flexible than the 1/8" which will be important for the smaller section joints.  Cork on woodwind instruments is usually sanded to make it slightly tapered so I can try that if necessary to make it easier to slide together.  I am almost ready to assemble the sleeves for the first joint so I will see.  

--Nathan, TX. Hire the lazy man. He may not do as much work but that's because he will find a better way.