MikeR, If you would like to be a counselor for any BSA Merit Badge, we would love to have you.
You will need to register as an adult volunteer, but since you are a counselor, it won't cost anything. Pick up a registration form at your nearest Troop or Council office.
In our district, we require the counselors to take a one-hour course on how to be an effective Merit Badge counselor. It's a piece of cake.
Good Luck!