If you are looking for a good quality Omni-wheel that is non-marking you could try some of these:
http://www.rotacaster.com.au/shop/12...ble---r2/index
They are 125mm in diameter and you will need to either machine or 3D print your own hub depending on your application.
They are designed to be non-marking as they primarily used for handcarts and conveyors, they come in two different durometers 85 and 95A so don't have a huge amount of grip but should be very durable in your application.
__________________
Sponsors, parents, students and mentors love helping teams succeed. Denso Throttle motors also want to help, don't break their hearts.
REDBOX(gearbox for the throttle motor)
Facebook