N9803Z, a C206 operates frequently here in/out of GRR under the call sign 'Flint ##'.
After some research, it looks like call sign Flint are DEA aircraft. N9803Z is registered to Freelance Air out of Atlanta, GA. Their physical address is a post office in Atlanta. Reminds me of Southern Air Transport from years past, a front company for the CIA.
Here's Freelance Air's fleet, a smattering of C206's, C210's and a few MD/ Hughes 369's: