Adorama has one of the few third-party lenses for the RF mount as their Deal of the Day. The Venus 12mm f/2.8 Zero-D Ultra-Wide Angle is $899 (Reg $999) today only. You can also get the lens in the EF mount.
Lens Mount: Canon EOS RF / Canon EOS EF
Fixed Focal Length: Focal Length: 12mm
Lens Type: Wide Angle Lens
Image Stabilization: Image Stabilization: No
Special Features: Aspherical
Venus 12mm f/2.8 Zero-D Ultra-Wide Angle for EF and RF $899 (Reg $999)