You can find the admin log files in the /noncgi/BanLists/ directory. They're there for historical purposes. <img src="https://www.ubbcentral.com/boards/images/graemlins/smile.gif" alt="" />
Note that the file contains information that may not be in an immediately useful format, and is mainly meant to serve as a diagnostic tool after an event has occured.
According to https://www.ubbdev.com/ubb/ultimatebb.php/topic/8/3690.html the post count is stored on the 8th line of the the member record in /members/membernumber.cgi file, replacing member number with the 0 padded file such as 00000123.cgi.
That is the only place that the post count for a member is stored. Your best bet would be to estimate their post count and bump it back to that.