I really like the looks of the white corian round butt to square butt conversion grips for N-frame, that Collins makes. I plan on putting them on my 629-4 Mountain Gun. These are the only conversion grips I've seen that leave the front and back of the grip frame exposed similar to magnas but with a more streamlined look.
I've worked a lot with corian. Made some grips for a single six, and several custom counter tops. It's some rugged stuff that should make great grips. It can chip if dropped, but it's more dense and tough than the typical Ajax polymer grip material, at least in my experience.