alias allnicks {
var %i = 1, %n, %chan = $iif($1 ischan,$1,$chan)
while ($nick(%chan,%i)) {
var %n = %n $v1
inc %i
}
if ($isid) return %n
msg %chan %n
}

To just get all nicknames, use $allnicks(#channel) or $allnicks if you're in the correct window/event, to send a message to the channel with only all nicks: /allnicks #channel

You can probably adapt it somewhat to your needs...