Tokina SZX 400mm f/8 Reflex MF Lens for Canon EF SZXMF400-C B&H
A bit of history about Canon and catadioptric (mirror) lenses
Catadioptric mirror lenses: Canon EOS M Talk Forum: Digital Photography Review
Samyang Reflex 300mm F/6.3 Umc Cs Camera Lens Aps-c Format Catadioptric Telephoto For Sony E/a Canon M Fujifilm Xmft Nikon F - Camera Lenses - AliExpress
Mirror Lenses - how good? Tamron 500/8 SP vs Canon 500/4.5L
New TOKINA SZ 500mm f/8 Reflex MF Lens - CANON EF Mount Catadioptric ManualFocus 4961607264041 | eBay
Keppler's Vault 61: Mirror Lenses - mike eckman dot com