Wheels & Casters

Where did you source the wheels that go on the motor and the little ball-caster?

Apologies if I missed this in the other documentation posted here.

_Edit: I found the link to the Wheels via your Instructables page for this project. I see that Pololu also sells ball casters. Can you tell me what size of ball caster you used for this? Or if you did not get those via Pololu?_