B&H has used Canon RF 100-500mm L and RF 100-400mm IS USM Lenses in stock.
B&H has a pair of used Canon EF 300mm F2.8 L IS II Lenses in stock.
Also, B&H has used Canon EOS R6, Alpha 1, and Alpha 7 IV cameras in stock.
Learn more:
Canon EOS R6 Review
Canon RF 100-400mm F5.6-8 IS USM Lens Review
Canon RF 100-500mm F4.5-7.1 L IS USM Lens Review
Canon EF 300mm f/2.8L IS II USM Lens Review
Sony Alpha 1 Review
Sony Alpha 7 IV Review