Are you saying you can't find the Roaming folder, or that roaming doesn't have the folder? From within mIRC, this shows the exact folder name where mirc.ini is located, and is the folder your quote was intended to find:

//echo -a $mircdir

It's possible for this folder to be somewhere else, because if you install mIRC into C:\MIRC\ and had moved the mirc.ini there before starting the program, then it uses that folder instead of roaming.