Some organization have policies in place that prevent third-party applications (like Drone) from accessing the organization’s data. If you are not seeing organization repositories in Drone this is probably the root cause.
Navigate to your application authorizations in your GitHub account settings (see screenshot below). You will see a list of all organizations and whether or not they have authorized access to Drone. You may be able to manually grant access, or you may need to request that an organization administrator grant access.
Once you update organization access, return to your Drone home screen and click the sync button. This will synchronize your account and you should now see the organization repositories appear in your list or search bar.