I've been using a Leopold FC210TP for a couple years now and I'm very happy with it. (I got it off
Massdrop, but I see
Mechanicalkeyboards.com also has some.) Well built and I've really gotten used to the extra keys on the top row.
Big caveat with that recommendation though, it outputs the same keystrokes as the number row on a keyboard, not the standard keypad codes. As I use it for data entry and not gaming, it doesn't bother me at all. For others who want the differentiated codes, it's a complete show stopper. Do your research and know its limitations, but if you don't need the actual keypad codes, it's fantastic.
Also getting 3rd party keycaps that have support for the extra row is a little hit or miss. Some include it, some don't.