I've been looking for 3/8" tubing to change my watercooling loop and it seems that crazypc.com has a large assortment of tubings which one would be the 3/8" one? and which would be the 1/2" one?
http://www.crazypc.com/products/cooling/reservoirs.htm#tubing
http://www.crazypc.com/products/cooling/reservoirs.htm#tubing