You could try Fibraplex. They used to, and still do if I read their site correctly, make a 5/8" diameter tarp pole that might be stout enough for that height. I would send them an email about it - they called it the "Pinnacle" tarp pole, and they still show some versions of it in their price list. Look here:
and sctroll down to replacement pole sets; you'll see Pinnacle 62 and Pinnacle 48. The question will be whether you can get a custom pole with that same tubing, and whether it would be stiff enough for that height.
Also, Kelty makes some adjustable poles:
that might work for you. another idea is an avalanche probe. You can get various lengths and diameters and weights, in aluminum and also carbon I think. I know some guys who use them as mid poles for ski trips, since they already have them on board.