What are you trying to do specifically?
You can use $ialchan() to find host on a given channel, if you want to know which host from a given channel A is also on a given channel B, you can just use a while loop:
alias checkhosts {
var %A $1,%B $2,%i 1,%m
while ($ialchan(*,%A,%i) != $null) {
%m = $v1
if ($ialchan(%m,%B,0)) {
echo -a host %m on %A is also on %B -- nick on %A : $ialchan(%m,%A,1).nick -- nick on %B : $ialchan(%m,%B,1).nick
}
inc %i
}
}
Type /checkhosts #channelA #channelB
Note that multiple nickname could belong to a given host, the code will only return the first one.
Edit: looks like you were talking about another kind of 'host'