I also would like to know this. I live in Woodbridge, VA, but I'd do just about anything to get rid of my large MDF box for a "different" shape. I looked in the phone book, and there were some construction supply stores in Manassas, I'll have to give them a call sometime because I was running out the door at the time.
For new sonotube, I can only recommend checking the yellow pages under concrete construction supply houses or Sonoco's website for area distibutors. I just finished a Shiva sub and have about a 6' piece of 18" sonotube leftover. I originally got a 9' piece from a fellow HTF member so it's only fitting that my leftovers should help another member. If your interested let me know. I'm in Arlington. - Kevin
I got mine in springfield, i forget the name of the place, but it was under "concrete supply" on backlick road in springfield... they had a large variety of sizes, w/ decent pricing...
I don't know the name of the place but my brother found a place in Manassas that cut his to size at no extra charge. I think he paid $23 for 46" of 16" diameter tube.