https://hackaday.com/2020/05/21/linux-fu-alternative-shells/
There's no such extant thing as "pdksh" anymore; development has mostly been picked up by mksh, along with the OpenBSD pdksh fork. mksh can be found at: https://www.mirbsd.org/mksh.htm and some portable OpenBSD versions are available at https://github.com/dimkr/loksh and https://github.com/ibara/oksh - of these mksh is probably the most featureful and useful, and is a mostly drop-in replacement for any ksh88/POSIX sh script or interactive environment.
Note, however, that pdksh derivatives are all more like the classical "ksh88" than "ksh93." The Korn shell grew a number of very useful features - associative arrays, floating point math, etc. - in the newer ksh93 version. Bash has adopted some of these, but not all, and the pdksh continuations/clones will likely stick with ksh88 compatibility. The old AT&T AST repo has relatively up-to-date (and open source) ksh93: https://github.com/att/ast and the ksh2020 branch has a build system not stuck in 199