In OpenBSD 6.3, zynaddsubfx is neither in the ports tree nor in the binary repositories.
Quoting right from the
source code repository: "ZynAddSubFX is a fully featured musical software synthesizer for Linux, MacOS, BSD, and Windows."
So yes, there might not be any official packages for your package manager, but you can compile it yourself.
Maybe next time don't go ad-hominem at people when they don't entirely know what you are after and just want to help out by offering a solution that you can run natively on your operating system without DOSBox, even inside a modern DAW if you wish to do so. That's not being ignorant. Once again, I was not entirely sure if you assumed that SD2 would be a copy of another program, because that's what your sentence sounded like to me. It isn't, it's just an evolution of an earlier program Paul wrote, which basically does the same, just with less features.