The command to do what you're asking isn't built into mIRC itself. It would have been built into a script you used to use.
That being said, mIRC does provide the tools with which you can script a custom alias to do what you want.
You'll need to use what's called the IAL (Internal Address List). In plain terms, the IAL is a running list of addresses and the nicknames they belong to that your mIRC stores for people who speak in or join (etc) a channel that you're on. You will use the IAL with identifiers like $ial and/or $ialchan to find users. If you'd like to try making your own, good for you! There are channels like #HelpDesk on DALnet that can help you make your own if you're up to the challenge.
You'll need to be at least a novice scripter to do this, so in case you're not one, I've included my version of what you want below. To use it, make sure your IAL and remote scripts are on by typing "/ial on" and "/remote on" in any mIRC window just once each (and not every time you open mIRC). After that, in mIRC hit ALT + R. This will bring up a window for editing scripts. Go to File and "New." This will create a new script file in which you can write new scripts. There, paste what you see below. (The script is a little old, so it uses some obsolete scripting methods, but it works.)
Use the script by right clicking in a channel and going to "Scan for users using an address." It will scan all channels for a hostmask matching your input. Note that if you use it while you're in very large channels, your mIRC may freeze momentarily. I've left the script's variables fully named and the script fully laid out on many lines so you can tweak it easily if you like.
**START COPY/PASTE**
menu channel {
Scan for users using an address:scanhost $$?="Enter hostmask to scan for (ex: *ipt.aol.com or *aol*)"
}
alias scanhost {
if (!$1) { echo 4 -i2a $alertprefix * /scanhost Error - no input }
echo 12 -i2a -
echo 12 -i2a --- Scanning channels for hostmasks matching " $+ $1 $+ "
set %temp.scanhost.colors.all 2 3 4 5 6 7 10 13 14 15
set %temp.scanhost.chans.tot $chan(0)
set %temp.scanhost.chans.now 0
set %temp.scanhost.input $+(*,$1,*)
while (%temp.scanhost.chans.now < %temp.scanhost.chans.tot) {
inc %temp.scanhost.chans.now
set %temp.scanhost.users.tot $nick($chan(%temp.scanhost.chans.now),0)
set %temp.scanhost.users.now 0
:selectcolor
set %temp.scanhost.colors.now $gettok(%temp.scanhost.colors.all,$rand(1,$gettok(%temp.scanhost.colors.all,0,32)),32)
if (%temp.scanhost.colors.last == %temp.scanhost.colors.now) goto selectcolor
echo %temp.scanhost.colors.now -i2a -- Scanning $chan(%temp.scanhost.chans.now) $+ ...
while (%temp.scanhost.users.now < %temp.scanhost.users.tot) {
inc %temp.scanhost.users.now
if (%temp.scanhost.input iswm $address($nick($chan(%temp.scanhost.chans.now),%temp.scanhost.users.now),5)) { echo %temp.scanhost.colors.now -i2a - Match Found: $nick($chan(%temp.scanhost.chans.now),%temp.scanhost.users.now) ( $+ $gettok($address($nick($chan(%temp.scanhost.chans.now),%temp.scanhost.users.now),5),2,33) $+ ) | inc %temp.scanhost. [ $+ [ $chan(%temp.scanhost.chans.now) ] $+ ] .totfound }
set %temp.scanhost.colors.last %temp.scanhost.colors.now
}
if (!%temp.scanhost. [ $+ [ $chan(%temp.scanhost.chans.now) ] $+ ] .totfound) { echo %temp.scanhost.colors.now -i2a - No Matches Found }
}
unset %temp.scanhost.*
echo 12 -i2a --- Scanning complete
echo 12 -i2a -
}
**END COPY/PASTE**
Enjoy.
