I found some tubes on http://www.hobbysuperstore.com/browse.cfm/2,696.html which can be used as stuff tube in boats...

Hope this info is helpful...

sure.. but inexpensive, but effective option is.. the hydraulic pipe lines of a lorry or a bus.. can take from replaced or discared.. or can buy new for a little money.. stiff.. strong.. lasts for a lifetime.. and can also add a greasing tube by soldering.. a vertical tube easily.. 

these brass  and SS tubes ( even pure copper) can  befound locally at any metal merchant.. also costs less than quoted by the link....

@alok: try lohar chawl in mumbai....!

Vish.. SS and brass are for maximum pecision.. can also be use carbon fibre tubes.. with brass busings each side.. with rubber O rings..

made a stuff tube from 2 gel pens for 4mm driveshaft!

Hope it works

Suggestions/comments welcome...

Went to loharchawl in mumbai and bought brass stuff tube for 4mm shaft,bought 3.2mm Int.Diam. stuff tube also with 3mm steel shaft...Will make motor couplings and post pics...i.e. 3mm-4mm female to female coupling,etc.

Thanks for taking all the effort Alok!

Its was out of sheer passion for RC!

Alok.. one of the easy and effective way to make a water tight stuff tube for boats is straight from ball point pen bodies with brass bushings.. 99% of my boats are equipped with this idea, and most of them are working in daily basis, from Academies, and Engineering colleges.. and i am already posted a detailed build log on this after knowing its goodness and reliablity.. inexpensive but 1000% effective.. here is the link..
http://www.rcindia.org/boats/make-a-propeller-shaft-and-outer-tube-our-own-for-our-boats/