Use MM7View to look within events.lod, at the file npcdist.txt. It contains the data for which hirelings appear where. (The order of the areas must be discerened from other files.) If you like, export it, then edit it in a text editor. After "Gate Master," change the third "0" to a "10". (The third row is Erathia.) Save it, and import the edited npcdist.txt back into events.lod. Gate Masters will appear in Erathia.

(This is mostly from memory, but I can take the time to double-check if there's difficulty.)

Always back up game files before you change them.

And it's probably easier just to search a different region.

BV