I replace the tube every time. Last time I changed my rear I checked the rubber band and it looked fine so I let that slide. I got my tire/tube from Jakewilson.com. They might have the tube you need. Funny that some online places have one thing and not the other. It's hard to do one-stop shopping sometimes.
Exactly what I am running into! Have the tire, rubber strip, dyna bead kit and spoons in my Cart with them but no tube available with the side mount. Will buy that at dealer since it is not available but sure would have been nice to buy it all on-line and save the trip.