Bobcat composite airtube.

I have only seen carbon fiber wrapped bottles, not tubes. As far as I know manufacturing high pressure carbon fiber wrapped bottles requires a completely different prosses than manufacturing aluminium tubes. To have a company to make carbon fiber wrapped bottles for a given size probably require to mass produse them in big quantities, othervise they would be very expensive. Aluminium tubes are easier to produse, and can be made easier with different dimensions.

If you own a .25 or .30 bobcat, you can attach the shorter 300cc tube which is on the smaller caliber bobcats. Maybe there is even smaller tubes with same threads available?