You'd need to know the difference between GMT (or your local timezone) and the timezone of where you wanted, and add/subtract that from $gmt (or $ctime if you use your local timezone)
Bear in mind too, that daylight savings will play a part on both ends of the equation. For your own timezone you can use $daylight to offset that.
Example: Anchorage, Alaska, is GMT -9 hours, plus 1 hour (DST). (GMT -9 +1) = GMT - 8(hours)
//echo -a Anchorage, Alaska: $time($calc($gmt - (8 * 60 * 60)),HH:nn:ss)
