These search engines are a great place to start your OER search, especially if you're not tied to textbooks. They search across a variety of OER collections, databases, and repositories to make your search a bit easier.
OASIS https://oasis.geneseo.edu/
Openly Available Sources Integrated Search (OASIS) is a search tool that aims to make the discovery of open content easier. OASIS currently searches open content from 98 different sources and contains 368,234 records. Created by SUNY Geneseo's Milne Library.
Mason OER Metafinder (MOM)-Provides a simultaneous search across 20 different sources of open educational materials. Created by George Mason University.
