The new released EF 100-400mm f/4.5-5.6L IS II USM lens is a great lens according to latest reviews. Currently, most US stores are out of stock for this lens. Below are authorized dealers that has this lens in stock and ready to ship.
EF 100-400mm f/4.5-5.6L IS II USM lens – at Authorized Dealers via Amazon.com
EF 100-400mm f/4.5-5.6L IS II USM lens – at Authorized Dealers via eBay.com
Currently, B&H Photo Video and Adorama don’t have this lens in stock yet, you can pre-order if you need.