Brent,
No 20km grids are being distributed from the 20-km RUC model at this time. The 236-grid data is generated from the 20-km RUC, even though it is at 40km resolution.
If you think it would useful if the 20km grids from the RUC were distributed at least from the surface and precipitation fields (we at FSL do), you or your company/station could request this through the NOAA/NWS.
Stan