As far as I could find information about "http://ircbl.org", it is most likely closed from general remote use and works only by invitation or after registering on their resource. (I could be wrong). But I was unable to find their DNSBL servers that check for bad IP addresses. Only if try to add an additional piece of code to this script that could check the addresses of attackers through this web page. But this will already be a workaround and not entirely reliable, because the resource owners can block access to the site due to frequent requests from the bot to this page.
Fortunately, I think this is not really necessary, because you can create your own large list from free of DNSBL servers to protect your chat. And this will work no less efficiently than that site. The main thing is to keep your list compact, so that the check happens quickly enough (within 1 second) and it is important to minimize the false positives of the script by fine tuning.
The lists themselves can be searched through search engines and thus you can to collect a working and reliable list of DNSBL servers in this script. The main thing is to test them thoroughly, because not everyone can be working or they can give false responses to both normal and bad IP addresses, therefore to detect real proxies, it is necessary to set work only with those numerical answers that give 99.9% correct results.
For example: "dnsbl.dronebl.org 4,5,6,7,8,9,10,13,15,17,255" - during my testing with this DNSBL server false positive was were with numeric responses "1,2,3,11,12,14,16", therefore they do absent in a numeric comma-separated list. The numeric response "255" catches unknown and unsigned (without a signature) addresses as proxy found through this server, which can also be a false positive, but I included it this the list just in case.