How do I obtain permission to fly an airplane that isn't airworthy?
You must request a Special Flight Permit from the nearest FSDO (Flight Standards District Office).

You'll need to fill out Form 8130-6, Application for U.S. Airworthiness, appropriately calling out the reasons you need a SFP (ferry flight, etc). Once the form is submitted, you may be subject to an inspection by an FAA official or representative, verifying that your aircraft is in fact in a condition for safe operation.

Avemco, the insurance company, has a good article on ferry permits that might be worth an extended read and which I don't intend to copy here.