You can usually find them at a hardware store. They are supply line hoses. Braided nylon hose. Just be sure to get the right size.......there is inner diameter measurements, and outer diameter measurements.
If you can find blue nylon braided hoses please let us know where. I have only been able to find clear hoses. If you can't find blue they can be dyed I would recommend RIT Navy Blue powder. If the powder doesn't work give the liquid a shot. They will probably have to sit for about 24 hours in the dye before it reaches the correct color.
(Disclaimer) this is the technique for dying the hoses that I have read here on TDH that seems to have the best results. My blue hoses came with the gauntlet kit that I purchased from Cruzer so I have not tested this method.
This is the thread for dying them. http://www.thedentedhelmet.com/f28/how-do-i-dye-jango-fett-tubes-44381/?highlight=jango+hose
As far as the diameter goes I believe it's 1/2" OD I'll double check mine when I get home.