I have one. I don't have a recent pic of it, but here's a shot I took in 2014.
I got the PC-4 calculator first, and searched in vain for the interface by itself. I finally saw an auction on eBay with the PC-4 AND the interface, so I bought the PC-4 a second time just because it was so hard to find the interface.
Here's the Equipment page for the item(s):
https://www.gbfans.com/equipment/other/ ... alculator/ It IS possible to build an interface from scratch, as odd as it may sound. I can't find the thread at the moment, and the photo links might be dead even when I do, but sometime prior to 2014, James Fincher of Fincher Technologies (username jimfin on this forum) used some Facebook photos of mine and a couple of measurements that I provided to make one entirely by hand.
He sourced the exact power button, even had the correct number of pins on the interior to go into the PC-4. I held the thing in my hands before he told me it was hand-made, and I couldn't tell the difference between that one and my factory-made one. I even asked him where he found another real one, then my jaw dropped when he said it was custom-built.
Alex