We have a monopod here at work which extends to 6-7 metres. Made by Nikon and we use it offshore for supporting HD video cameras when filming in confined spaces etc..trouble is, is cost more than most cameras!!! Around £400!!!
It is extremely heavy (stability) and cumbesome and packs down into a tube about 1.5 metres long by about 25cm diameter. It looks like a radio mast when up!
What you could possibly do is buy one of these
http://www.fostersofbirmingham.co.uk/ST28425 which has a bog standard 3/8" thread one side and a camera thread the other and have a blacksmith make up a sectioned pole or weld a bankstick threaded head to something.
You could buy the butt sections of a carp pole as these are strong and rigid, If you bought say sections 8, 7, 6, 5 that would give you about 7 metres with a diameter of about an inch at the "tip". Here is a link to sections of a cheap but strong carbon carp pole.
http://www.fishingspares.co.uk/index.php?cPath=1_50_159 If you went for my pole you would be about £400 lol
Mike,
Everyone likes lightweight tripods, but you really want a heavy one. The heavier the pod, the more stable it is. Again, our ones at work must be in the order of 15-20 pounds in weight for professional camera work.
However, for DSLRs if you use a cable release then you can get away with a lighter pod. Mine is light because if comes fishing with me in a rucsack, but I hang the rucsack from it to add stability.