Ideas for a GT2 gearwheel

Hey guys. Im currently designing a machine for my bachelor thesis. Ive got a rotary chuck in which a tube is clamped and fed axialy. I want to rotate the whole chuck via a GT2 belt. My problem is, that there are no GT2 gearwheels with large diameters. My tube is 150mm in diameter and the chuck somewere at 250mm. Therefore the gearwheel must be ~250mm in diameter.

Milling the teeth would be to expensive for my construction.

Du you maybe have an idea?

Sorry for my bad english, its not my first language.