Reinstall mIRC or copy the popups.ini from the "defaults\scripts" directory in the mIRC dir (Appdata directory if it's not in Program Files), and put it in the mIRC directory. You can type //run $mircdir in mIRC to get to this directory. Load the popups in Alt+P (File -> Load...)
These are (as the directory says) the default popups that come with mIRC and should be what you're looking for.
