Huh, looks like every(?) issue of MRR is on archive dot org. And it wasn't upped by anyone that has anything to do with the zine & isn't linked from the MRR website. A cursory sampling of the record reviews over time seems to suggest always sub-200 new releases a month.

https://archive.org/details/maximumrnr?lang=en&tab=collection&sort=title&and%5B%5D=firstTitle%3AM