Tap your network. Ask your colleagues. This is the best place to start when looking for an Instructional Designer to join your team.
Instructional Designers come in all different forms: some may be focused on only doing technical training development; others may have a specific area of expertise; others may be generalist, and some may only focus on management or leadership development.
Whomever you looking to hire begin your search with your network, next to local HR, Training, and OD associations, and then search job boards and post on LinkedIn and other sites. Good luck in your search!