The IRS and the tax forms do not ask for a NAICS code.  They ask for Business Activity Codes (which is based on NAICS, but often more broad) that are in the IRS Publications.

For example, here is the list from Schedule C, which does NOT include the code that you are asking for:

https://www.irs.gov/pub/irs-pdf/i1040sc.pdf#page=17

No. Provide an appropriate number for the list IRS provides.

"722330"

Go UP a level until you find what would be the upper or parent code.