Answer:
There are some senior members of the community who have the rights to give us supervisor rights.
If you consistently post genuine answers to a particular category, one of the senior members would definitely spot you. If the other supervisors feel that you are good enough to be a super, you will be given an opportunity.
If you want, you can talk to any of the supervisors and express your intention which they would consider after you have proved your knowledge & passion for the site.