One way is to post on specialized art forums or websites. There are many places online where artists showcase their work and might be interested in collaborating.
You could also attend comic conventions. There, you have the chance to meet artists in person and discuss potential partnerships. It's a great opportunity to see their style up close and gauge if it's a good fit for your project.
Another option is to reach out to art schools or colleges. Sometimes, students or recent graduates are looking for projects to build their portfolios and might be enthusiastic about working with you.