There is a merit badge counselor list available for district and council members available in the Roster tool in my.scouting.org.
New Merit Badge Counselor list report in my.scouting.org 3 for council members, district committee members and commissioners.
Log into http://my.scouting.org 3
Go to your council or district
Click on Roster
Click on Reports
Depending on how your council registers your MBCs they may only show on the council level report.
To find who counsels a particular badge, say, swimming:
Export the list to Excel. Click on the header row, Turn filters on, and click on the pull down in the Merit Badges column. Type in the name of the badge you are looking for.