Take a look at Julien--they might make one(?).

Although I cannot give you any sources for a zero-radius drop-in sink, I would urge you to reconsider the zero-radius configuration. I have a zero-radius single-bowl undermount sink and I must admit that it is one of the choices in my kitchen remodel that I really regret. Although it looks very sharp, it is very impractical as it does not seem to eliminate food waste properly and its sharp corners tend to accumulate grime and are very difficult to clean. I much preferred my Blanco D-bowl sink in my previous kitchen as it stayed quite clean without much effort.