It's a designer bespoke dress by Jenny Packham. Theres no way "to get it".
But you can check out other Jenny Packham's dresses here https://www.net-a-porter.com/en-gb/shop/designer/jenny-packham?Skimlinks.com=Skimlinks.com&cm_mmc=LinkshareUK-_-TnL5HPStwNw-_-Custom-_-LinkBuilder&dScroll=0&dclid=CjgKEAjwk6P2BRDX-JXL3rL50jkSJAB0Kc4-9WSxnxjgmVQIXRgQMlXHIrjOOKdQ7_SkucHof72BifD_BwE&image_view=product&npp=60&siteID=TnL5HPStwNw-WzmiU3xFRRmBWQvf9iuu5w and here https://www.jennypackham.com/