Perform targeted outreach. If you know someone you’d like to work with, you could contact designers directly. In case they are unavailable, you can ask to refer a colleague.
Browse design communities where UX/UI designers share portfolios and showcase their work. Dribble and Behance are probably the most well-known platforms of this kind.
Check out some popular freelance platforms like Fiverr or Upwork. They usually have extensive networks and some low-cost offerings.
Try using job boards specializing in UX design, e.g. UX Jobs Board, Toptal, or Just UX Jobs.
Choose a successful design subscription – a global community like Awesomic with some top experts. They can help you find a UI/UX designer by using powerful algorithms or customer manager help.