I am the owner, developer and maintainer of the ircbl.org. The public dns server you can use for your RBL requests is rbl.ircbl.org.
I have now updated the ircbl.org website with an 'about' page, which has more information about the ircbl RBL and who can use it.
There's no restrictions in place, unless you have to do dozens requests/second, then I may need to whitelist your server's ip on my dns server.
for more info.
Let me know if you have any questions.