Most DDoS attacks directed at IRC networks are not government related. IRC networks have a long and proud history of being one of the most DDoS-prone targets on the internet.
To my understanding to take down an IRC server doesn't even need to be a DDOS (Distrubuted Denial of Service) AKA multiple of computers and connections. One good DoS (Denial of Service) AKA one computer one connection, is all it takes to take it down.
It's a matter of bandwidth. If a single malicious actor can clog the the IRC server's uplink on the internet facing side of their firewall yes, otherwise no.
It's probably the case that lots of people try that, but unless the IRC server(s) are being hosted on their home network then I doubt one or two computers could bring a whole IRC network down.