Cobra trailer wing dolly plastic sidewall rollers?

When I was at the Perry contest last week, another pilot mentioned to me that the wing dolly plastic rollers that run in side channels to keep the dolly upright had worn out, causing his wing dollies to bind when rolling in/out of the trailer. We looked at mine, and they are badly worn as well, so I'd like to get replacements.

Does anyone happen to know the dimensions and material for these items? I'd rather get the parts from McMaster-Carr if available, as I suspect I could get them much cheaper/faster than all the way from the factory.

TIA,

Frank