Metropolitan Statistical Areas (MSAs) in the U.S. are comprised of counties. Within MSAs, the Census Bureeau makes a distinction between "Central" and "Outlying" counties: https://www.census.gov/programs-surveys/metro-micro/about.html
I have searched far and wide for a user friendly (data analysis friendly) list of counties that contains information for their central/outlying status within MSAs. Unfortunately, I cannot find anything resembling a spreadsheet or data table.
I did find a list in an OMB bulletin https://www.whitehouse.gov/wp-content/uploads/2020/03/Bulletin-20-01.pdf?# , beginning on page 41, that contains the relevant information, but I am unable to extract this information in a systematic manner.
Does a spreadsheet/data table of this information exist anywhere?