The idea of using copper brake line sounds interesting.  3/16" is
the smallest I can find in casual searching.  It looks like it is about
$1 a foot, which seems reasonable.

Another possibility occurred to me but it might be very expensive.  Tin
tubing has been used for many years in food and beverage applications.
All soda fountain tubing was tin before stainless steel took over the
market.

I have some old tubing taken out of antique fountain heads and it looks
almost identical to lead tubing once it develops a patina.  When new it
is quite bright.  I have several rolls of tin foil and they look a lot
like lead where exposed.  The unexposed parts are still very shiny after
50 years or so.  It looks a lot like nickel but it should be easy to
find a formula for a dark patina.

This company sells tin tubing in a variety of dimensions and will do
custom orders as well.  The 99% might be affordable?  Tin tubing is
very easy to bend without kinking.  Tin is also a lot stronger than
lead and a much thinner wall could probably be used if the increased
interior volume is not a problem.

https://www.americanelements.com/tin-tube-7440-31-5 

Spencer Chase
Garberville, Calif.
http://www.spencerserolls.com/