Pipe the output of robocopy through find, with the /L switch to only list what would be copied.
Robocopy can filter by days. Don't change anything - just run it in the folder you need to count.
robocopy . c:\magic /maxage:30 /fp /ndl /njh /njs /xx /L |find /c ":">> %srclog%
This portion of yours looks like a Linux command using the find on there, and not Windows.
(find . -type f -mtime +30 dir "dir\")