Maybe a siding supplier?  It is pretty hard to find.  I have a couple of pieces of the lighter Canadian pipe, but since I bought it I haven't come across it again.  10 years have passed and I live in Canada.  I have never even seen the thicker US pipe on my travels to the southern Detroit area, or Fla, and Georgia either.  I have heard of a vinyl fence post that may work, but is smaller, and aluminum pipe being used (?)