Since campaign passes were introduced, several troops are always cash-exclusive, as they only become freely available, when the next bunch is already included into the game.
So it would require paying money.
(P.S.: Suprised, that some posters up there a year and a half ago were asking for a Zul Goth achievement, as there already has been one since the troop exists on Steam. I thought, those were identical on all systems.)