Google Advanced search as a great way to start out a search for OERs. Just remember to choose the license type near the bottom of the screen.
Drawbacks:

Merlot is one of the oldest repositories of OERs. It has an entire community devoted to collecting OERs for learning world languages. The platform also offers peer reviews of many learning objects, and a rating system for general users. Materials are easily sorted into target languages for easy browsing.
Challenges:
OER Commons lets you search, find, save, remix and contribute OER.
Lots of ways to search! Check out these collections:
Curriki is a repository that mostly focuses on STEM materials for K-12 educators, but do have some materials for language learning and adult learners, including community college resources. It lacks a decent browse search, so here are some canned searches to get started.
With an account, you can collect resources you are interested in, create a personal library, join groups of like-minded teachers, and create and upload new material. Curriki has a review team that is available to vet resources.
Here are some other sites that might help you with an OER Language course.