There are a couple of datasets at NOAA's National Centers for Environmental Information that can help. NDFD is good, but it is based on forecast model output and not station data ("ground truth"). For starters I would use the U.S. Local Climatological Data (LCD). You could use the Min/Max dry bulb temperature, but it has several climatological data types ...
There are several web applications the can calculate IRGF from latitude / longitude coordinates
These sites are documented in the IGRF-12 online data products section of this paper:
From my similar experience in a weeks-long search for an alternative to NOAA's CLASS archive, the answer is apparently no, or not yet. And AWS only has images, not other relevant variables of interest e.g. aerosol optical depth values.
That said, here's GOES-R decoder instructions.
The GOES-R decoder supports the ingest and display of NOAAport provisional ...