you can eliminate a lot of the if-then statements. try this

ctcp *:unban:?: {
  if ($3 !ischan) { .msg $Nick You must select a channel. | halt }
  var %a = 0
  while (%a < $Ibl($3,0)) {
    inc %a
    if ($Ibl($3,%a) iswm $address($2,5)) { mode $3 -b $IfMatch }
  }
}