You want them to port a buggy irc client with a lot of security issues? X-Chat Aqua will do everything that mirc can do (you may just need to find the appropriate plug-in).
There's a bunch of them out there. X-Chat Aqua is one I haven't tried yet. I use Conversation myself, and I've used Colloquy in the past. I recalled both of those URLs from memory 🙂
I use ircle but I'm not entirely sure whether I would recommend it or not - I've used it for so long (6+ years) I really couldn't tell you what any other clients are like in comparison 🙂
Snak and ircle are good, but because they're shareware, they quit working after 30 days. As such, I'd have to suggest Colloquy. It's got all the same features, and it's free!