Hey there!
I don't know where exactly you are, but from within the US you can order it online here: http://www.hobbylinc.com/cgi-bin/s8.cgi?str_s=plastic+tubing
Other than that shops that sell materials for model kit building should have something like that as well. You don't have to use plastic tubing, by the way, you can also use brass tubing for both pieces instead.
