What about that EF 200-600mm f/4.5-5.6 IS from Canon?
Sony 200-600mm Lens Review: Wildlife Photography Field Test - Nature TTL
The Superzoom rumor: Canon EF 200-600mm f/4.5-5.6 L coming in 2018? - mirrorlessrumors
Sigma F4.5-6.3 DG OS HSM Sport - Teleobjetivo Zoom 60-600 mm para Canon, Color Negro : Amazon.es: Electrónica
Canon 90D + Tamron 150-600mm
Lente impermeable para SONY FE 200-600mm F5.6-6.3 G OSS, abrigo de camuflaje, cubierta de lluvia, funda protectora, tela de nailon para pistolas, 200-600 _ - AliExpress Mobile
Objetivo Canon EF 600mm f/4L IS III USM - Canon Spain
Canon EF 200-600mm f/4.5-5.6 IS lens set for 2016 release | Photoshop Actions and Lightroom Presets | MCP Actions™
Sony FE 200-600 mm f/5.6-6.3 G OSS - Full-Frame, Zoom, Superteleobjetivo G (SEL200600G) : Amazon.es: Electrónica
Canon 200-400mm f/4L IS vignetting - AlaskaPhotoGraphics