That is an entire cable. I just need a board-mount D-sub. We switched to the 3721 so I actually needed a 50-pin instead of 78-pin. I did some searching on my own, and apparently a 50-pin 3-row D-sub is a standard. I ordered a Harting 09665526612 from DigiKey and it fit.
https://www.digikey.com/en/products/detail/harting/09665526612/4322731?s=N4IgTCBcDaIJwDYEFZliQRggXQL5A