For example, there is a very active GMRS repeater in the county adjacent to me, but as far as I know, that repeater with its frequencies and PL tone are not listed in any way in the database.
Have you tried mygmrs.com?
I've found the GMRS listings on radio reference to be pretty slim. It relies on listeners posting info about the repeaters, and that's not always accurate, and absolutely doesn't catch all of them.
Also, since GMRS repeaters are considered 'private property', owners may choose to not share info. Your best bet may be to try mygmrs.com and contact the repeater owner for permission/info.