While using outside resources is essential to getting an organization to kick off the ideation process, mature organizations will, over time, learn to lead some of this internally.
Most organizations have an individual with either previous experience or a passion for a specific ideation methodology or approach.
One such approach could be using a framework that the organization used with an external consultancy. Another resource could using a published and documented framework like the one used by Google Ventures which is outlined in the book Sprint, by Jake Knapp.
Sample approaches for ideation can be seen in the Digital Continuum under the Labs and External Co-Creation elements.