You can get a distribution tarball suitable for installation from the release area.
If you are interested in modifying the software, you can clone the GIT repository:
https://github.com/michipili/bsdowl.git
If you are running a UNIX like system for which BSD Make is not available as a package, you should consider building it from source. For this, you should download bmake.tar.gz and mk.tar.gz distributd by Simon J. Garrety.
FreeBSD, NetBSD, OpenBSD and most Linux Distributions already provides BSD Make, wether as part of the base system or as a third party package.
It seems that BSD Make is also packaged for Cygwin, but some users experienced troubles with that package.