I use
www.canalrubber.com for my tubing needs cause they are local to me. They do say they serve customers nationwide though so if you can't find someone equivalent close to you, you can give them a try.
They carry many types of tubing, even food grade if you're leary of sucking on an unknown substance.
The only problem is that some of the tubing, especially the smaller sizes do not seem to be sold by the foot. They're not expensive but can you use a 25-100 foot coil?
As for shrink tubing, the only type I'm familiar with, did not seem suitable as it would collapse when bent limiting its versatility.