What is this double-drain piece called?
I am going to say that this was a purpose-built/proprietary drain assembly that was designed for and supplied with your special sink.
I have never seen one like that, and I have seen many many sink drains, p.o. plugs, pop-up assemblies, strainers, etc.
There are a lot of specialty plumbing parts available though. Like this one that I found when I Googled &quot;double basket strainer&quot;: