Found this local company in the Akron, Oh area that makes natural rubber tubing. So I called to place an order and they said to contact McMaster Carr, they sell their product. Here's a few links.
http://www.mcmaster.com/ search for "LATEX RUBBER TUBING" at McMaster Carr.
My friend replaced the tubing on his GUs with this product, and said it made a huge difference on the marks.
Thought some might be interested.