Adjusting some zoning restrictions and streamlining permitting processes to encourage more private development would have a quicker impact.

Here (and I'm assuming in most places), the condo association governs STR restrictions, not the local/county governments.

DM me and I can send you the schedule online for them if you want to come North, but I am also happy to connect you with a couple investors right in your area who are active and go to meetups in Monmouth.

-Are there legal restrictions on this in NC, such as the length of the option?

.- You might also look into staging the property or taking high-quality photos to make it more appealing online.- Another option is to list it on multiple platforms, including local real estate groups and social media.

I would go online and check other rentals in your area to see what other management companies are out there, and start contacting them.

Quote from @John Underwood: First thing to do is check with the city or county to make sure the ADU would be permitted to be a STR.The municipality has an application process but initial indication is that it's not overly restrictive in the area I'm looking at. 

It's online begging.

You also need an online presence—this is commonly one of the most important and not done step.

Some areas might have restrictions on renting portions of a home, especially basements.