I called the DC sheriff's office today. I asked to speak with the sheriff about a sign off for an NFA firearm with a Form 4. The receptionist told me that a different LT was in charge of that stuff and gave me his number. I called and left a message. I will try again tomorrow.

I am aware that the sheriff can delegate this responsibility to other officers, and may have a chance here with the LT rather than sheriff Weaver.

If the LT declines, I guess I can contact a judge or prosecuting DA.

If any of these authorities ask why I need the suppressor, I am planning to tell them that it makes competition and recreational shooting more enjoyable.
Any other suggestions for legitimate reasons?