Considering that the word commission is always followed by FOR, (ex.: commission for racial equality), the word commissioner requires the same preposition.
As for your next question, you could omit the preposition altogether.
ex. The hotel is just 20 miles south of Dallas.
You cannot say : the hotel is in the south of Dallas
that's because the hotel is in an area outside (American speakers would add 'of' here) Dallas, not within the city.
But you can say 'Guilford is in the south of England'
Hope this helps.
Student or Learner