Currently, 883 icons are available (27.02.2023). Special thanks to Maulana990.
You can get all the icons either as a library, include them directly in Android Studio or as single files.
Add the library in your dependencies and all the OneUI icon names start with ic_oui.
dependencies {
    // ...
    implementation 'io.github.oneuiproject:icons:<version>'
}Migration guide from 1.0.1 to 1.1.0
Pick oneui icons directly from Android Studio's Asset Studio by going to File > New > Vector Asset > Clip Art and searching for oui.
For this to work, you need to download material.zip and extract it to <android_sdk_dir>/icons/material/. Replace icons_metadata.txt and merge the contents of materialicons.
Default SDK location:
- Windows: 
C:/Users/<username>/AppData/Local/Android/Sdk/ - MacOS: 
/Users/<username>/Library/Android/sdk/ - Linux: 
/home/<username>/Android/Sdk/ 
After you've extracted the zip you can open the Asset Studio and find all the oneui icons by searching for oui.
Notes:
- The Asset Studio will add a tint to the drawable. Simply remove it if you need the colors.
 - Some icons might not work, in this case you can also get them from below. (I'm working on a fix)
 
If you're not using Android Studio or need them as a file you can get them all here.