I assume you found this thread by searching for the karaoke keyword, as you replied to a 9 year old thread, and he no longer posts, and probably no longer visits.
The link he showed lets you search for the karaoke keyword, but I assume it only searched the networks listed on that 'browse networks' link, and I don't know how recent their searches are.
It might be possible to find channels by searching in Google, but lots of hits would be old pages for channels no longer active. There might be mentions in Facebook too. In mIRC's Alt+E servers list, those list a lot of irc networks which are unrelated to each other, so they're not likely to know anything about channels at other networks. Once you've picked a network to join, you can use the /list icon or command to list channels, and you can restrict the list to show only channels containing your keyword. It's possible for channels to have a secret/private tag to prevent them appearing in the channel list, but you'd have a better idea whether karaoke channels often did that.