Tried these folks? http://www.jannsnetcraft.com/vinyl-plastic-tubing/
I've used them in the past for rod building stuff, ship fast.
Simple, straight forward no B.S. sorts. They've plastic and latex in assorted colors / sizes.
Natural latex can be easily stained to darker colors too.
I've anouther site (somewheres) that supplies natural colored latex in long lengthe up to 3/4" dia. I'll look and see if I can find it.
PS; Here it is, http://www.4fishin.com/surgical_tubing.htm
I've yet to order from them yet though.