that piece of tubing is not available separately from the rack. if there are no screw-in fittings on the ends it must just press into the rack. take a caliper (or an adjustable wrench - poor man's caliper) and place it on an undamaged area of you tubing. then measure the opening to get the approx tubing diameter. if it's something like 3/8's, 5/16's, 3/16's or 1/4" you can easily make a new tube from a piece of tubing you can purchase at the auto parts store, or hardware store. the hard part will be to get the old piece off, but one way or other i'm sure it can be done. you could probably cut the rusted tubing near the ends (assuming the ends are better shape than the center part) and replace the metal with plastic tubing. i believe the only purpose for this tube is to pass air back & forth between the two bellows (without getting dirt or water sucked inside) when you turn the wheels.
