You should be able to find rubber tubing in your area at a supplier of
pneumatic equipment for industrial use.  I would recommend a polyester
or polypropylene tube, or a vinyl perhaps, as they will not rot away as
quickly as rubber.  They may also have some sizes of brass and would
definitely have copper tube if you are using it where it is not
visible.

In the Toledo, Ohio, area near where I live I would try Airdraluics in
Waterville, or Midwest Fluid Power Co., also in Waterville.  If you are
not from that area look in the Yellow Pages under Fluid Power or
hydraulic and pneumatic.

Jack Steiner