Help needed

I have a Belgium made, Browning "Light Twelve" with a Deluxe Poly-Choke. I am sure the poly-choke was added on and is not original to the gun. But my problem is that I lost the little ball bearing (seat bearing) that goes under the C-clip spring (if that is what that is called).

Does anyone here know where I can get a new ball bearing to put back in it.

The only manufacture name on the choke is Hartford, Conn. Deluxe Poly-Choke.

Thanks for any help.