Couldn’t find any, not on asset store, not via googling. Was constantly getting either paid offers or not relevant things (such as details of #unity3d channel on freenode). IRC is so well-known protocol and chat is so common in games that I’m puzzled no one made free asset to do this.
I used this IRC library for C# to make a twitch bot for fun. Might be useful to you maybe 
It worked very well for what i was doing. ( Finding events that happen during a live stream by analyzing twitch chat in real-time )
https://github.com/SirCmpwn/ChatSharp
I believe it has everything you need to implement IRC chat in your game