Thanks.
It's a 15×8 PS/2 Access-IS keypad with two programmable layers. I've put thick Cherry POM/PBT keycaps on it, they make the MX Black switches feel almost like smoother reds. The programming software is a PITA to use, mostly because the front-end is flooded with weird bugs.
You can find such keypads on eBay (Access-IS is originally UK-based, thus UK eBay might be your best bet) or in the classifieds here or over at Deskthority. Tipro, Cherry Corp., Elcom or Desko make similar keyboards.