I need to pay the car insurance. My local surplus place gets these out of medical laser printers where they rotate a pol cube or a waveplate. Three have a half inch clear hole and the one with the waveplate (#4) is about 3/8ths inch. Put some plastic burst grating stock on them from One Stop, or have a lumia that spins from its center instead of its side. They have stepper motors on them with belt reduction or gear drives, so pick your favorite 20$ stepper motor driver kit and rock on. Or easily replace the stepper with a DC motor.
27$ each plus 7 dollars postal shipping in the US. Overseas buyers, note that you will have to pay actual shipping. Note these are big heavy blocks of aluminum with super stiff ball bearings to hold the prism.
Pol cubes are held in with a epoxy. A hammer makes fast work of removing them. I've found most of the pol cubes are IR or deep red, so don't count on reuse. Note they spun the pol cube to set course intensity in the printer, not to combine/split the light.
You cant buy the bearing or even think about milling the block for this price. Units 1,2,3 in the picture are fairly large, unit 4 is the tiny, thin, one.
The top two in the picture are gear driven, and the other two are belt driven.
Steve