Replacement 8 inch caster wheels (USA)?

[John Doe]

I can't find them on Amazon. Specifically, I need 8 inch caster
wheels.

I have compiled a few sites from earlier research, but more is
better.

http://enableyourlife.com/wheelchair-caster-wheel-assemblies.asp

http://www.edmond-wheelchair.com/8_x_1_ultralight_casters.htm

http://www.quickie-wheelchairs.com/category/Caster-Wheels/519

http://www.wheelchairparts.net/CATALOG_c316997.html

http://www.southwestmedical.com/category/Caster-Wheels/519

This is not spam. I am an active participant, hoping for other
suggestions, or critical opinions on the suggestions above.

Thanks.