I have completely run out of the large yellow tubing most commonly used.  I also use a samller blue tube with some success.

Can anybody refer me to the name of the product and the ultimate source, or somebody in the business of selling it?

Have you tried MBS Model Supply.  

Yeah, I buy stuff from Melvin at The Nats. 
I was hoping to find some sooner.  Maybe from flyer who's over-stocked of getting of the event.

You don't have to wait until the NATS. You can order it from Melvin, too.