If you have the JSON script for mIRC, this code will print out all users. Just need to type in the name of the stream (lowercase letters)

Code:
//jsonopen -ud viewers http://tmi.twitch.tv/group/user/streamname/chatters | var %i = 0 | var %user = $json(viewers,chatters,viewers,%i) | set %list | while (%user) { set %list %list %user | inc %i | var %user = $json(viewers,chatters,viewers,%i) } | echo -a %list