I can buy kits that comes with a few lengths of tubing, but I'd really like to have more so that I can produce quantities of noodles faster
Never pursued molecular gastronomy at home, but I can tell you that PVC piping is available at any plumbing supply shop. Probably far cheaper than when packaged in a molecular gastro kit too.
I was about to say "hardward store" but amysarah beat me to it!
Are you talking the thin type of tubing? An Aquarium store.