Is this Oregon? If so, it is my opinion that the Sheriff you are applying to is overstepping his authority by requiring you to prove need.

Oregon is a shall issue state and Sheriffs are required to issue licenses to residents of neighboring states that meet the eligibility requirements.

I would consult a lawyer and involve the State Attorney General and show this guy the error of his ways.

Just because police say "this is the way it is" does not make it necessarily so.