Amazon.com : High-Power 500mm/1000mm f/8 Manual Telephoto Lens for Sony a7r, a7s, a7, a6500, a6300, a6000, a5100, a5000, a3000, NEX-7, NEX-6, NEX-5T, NEX-5N, NEX-5R, 3N and other E-Mount Digital Mirrorless Cameras :
Opteka 500mm/1000mm Telephoto Lens Kit for Canon EF EOS 90D 80D 77D 70D 60D 50D | eBay
Opteka 500mm/1000mm Telephoto Lens for Canon EOS 4000D 2000D 1300D 1200D 1000D – MASER PET
High-Power 500mm/1000mm f/8 Manual Telephoto Lens for Nikon SLR Camera – Ruthy's Outlet
Opteka 500mm f/6.3 (with 2x- 1000mm) Telephoto Mirror Lens for Digital
Amazon.com : High-Power 500mm/1000mm f/8 Manual Telephoto Lens for Canon EOS 80D, EOS 90D, Rebel T3, T3i, T5, T5i, T6i, T6s, T7, T7I, T8I, SL3, EOS 60D, EOS 70D, EOS 5D, EOS5D
Bower 500mm/1000mm Telephoto Lens for Nikon D7000, D7100, D5200, D5000 – The Teds Store
Opteka High Definition 500mm / 1000mm f/8 Preset Telephoto Lens for Nikon Digital & Film SLR Cameras - Newegg.com
Super-powered 500mm/1000mm f/8.0 Manual Telephoto Lens (Black) with 2X Professional Multiplier for Canon EOS Digital SLR cameras and Deluxe Accessory Bundle with Xpix Cleaning Kit - Walmart.com