When I placed my order at RBI a couple of days ago for everything else I needed for my auto watering system they said they wouldn't have more 3/16 water tubing for about 2 weeks. So, I ended up ordering mine at:
http://www.snakemuseum.com/
That really sucked for me, because I had free shipping on my order at RBI. I ordered 30 feet of the tubing from the above and the shipping was just as much as the tubing... :(