A bit of history about Canon and catadioptric (mirror) lenses
300mm F6.3 Catadioptric Compact Telephoto for Mirrorless Cameras – Samyang US
SZX 500mm f/8 Reflex for Canon EF Mount – Tokina Lens USA
Mirror Lenses: Lightweight Super-Telephotos that Are Affordable | B&H eXplora
Buy 900mm F/8 Mirror Lens for Canon 1100D 550D 600D 650D 700D 1000D Digital Cameras+T2 Mount Online at Low Price in India | Non-brand Camera Reviews & Ratings - Amazon.in
T Mount 900mm F8 catadioptric lens Starlens SL900F8
Canon patents 400mm F5.6 catadioptric 'mirror' lens: Digital Photography Review
Canon: new L-series zoom and two telephotos for the masses by Jose Antunes - ProVideo Coalition
Patent: Is Canon planning to release catadioptric (mirror) super telephoto lenses?