Zero Motion Bearings

I've had another customer decide that there was too much play in the ScopeRoller caster assembly for his astrophotography needs, and I'm not one to let an issue like this stop me. He confirms that my solution to the problem of motion in the locking mechanism works--the play is now in the bearings of the caster itself. This is a few thousandths of an inch to perhaps a few hundredths of an inch. This may not sound like much, but .05" of motion here can turn into several trillion miles at the far end of the beam of light, so I am interested in finding a solution.

Obviously, a caster with zero motion when locked doesn't exist--unless it's made by the Frictionless Surface and Dimensionless Point Corporation. (You remember Frictionless Surfaces and Dimensionless Points from physics class, right?) But does anyone know of a maker of locking caster assemblies that might be so well made that applying a force of several pounds to a locked caster will result in a thousandth of an inch or less of motion? This is a tall order, and I would probably have to pay a lot more for such casters--and charge customers that need such perfection a tall price.