The debian/watch file is plainly out of date, and the homepage link https://crd.lbl.gov/~dhbailey/mpdist/ returns "Page not found".

https://www.davidhbailey.com/dhbsoftware/ has more information, including a pointer to https://github.com/BL-highprecision/QD where the latest upstream release 2.3.24 can be found.