Based on your
question, I'd suggest "813000" for "Religious, grantmaking, civic,
professional, & similar
organizations."
Sometimes the codes
aren't specific enough for certain occupations, and you just have to go with
what's closest.
Please see "Principal Business or Professional
Activity Codes" starting on page C-17 of the IRS' 2018 Instructions for
Schedule C if you'd like to search for a more appropriate code.