.... and now the conclusion to this episode....
Alloys and Components won out. Great place. I wrote them with my very minimal need stating that I understood if it wasn't enough for them to fuss with. They wrote right back, about $20 bucks for a 12" piece. The only thing is I wish I had known shipping was going to be 1-1/2 times the price of the rod. I would have bought a couple more to make better use of the tube.
In the end, I never could find a guideway rod that was 9/16". Seems not to be a standard size. Everywhere I looked jumped from 1/2" to 5/8".
Thanks again for all the help. This project is finally complete.