I had the same problem with the heater cable conduit I bought some tube off of a metal stockist and made my own !!
I don't suppose you remember the sizes do you? i'm in the same boat, mine was rotten so i cut it off and threw it away.
Not sure what the size is, will check and let you know, what i can remmember i would say maybe 20-25mm ?
I got some stainless 12mm tube off ebay http://www.ebay.co.uk/itm/390413613627?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1497.l2648