Hi guys, not sure if you know of these people or not...
www.thehighwaymen.co.uk - 01455 230736
They're a kite shop, and do a large amount of business in selling carbon fibre rod and tube, and also in fibre glass rod. The sizes start at 1mm, 0.5mm has to be specially ordered, and go up to 6 or 8mm.
They seem to be quite often far better priced than the usual model shops.
Cheers
Sean