Well I got the ring done, and here is the 3 stone cushion. It turned out great and she loves it and said yes this past weekend, when I surprised her in NY.
And now for the story. It was quite an adventure finding the best matching stone, and Mark Turnowski was a great help. I live in LA, but we were able to find a stone that macthed, and it looks great. Basically we had to figure out a way so that I could get the stones to a friend to look at, and Mark was very helpful. It all turned out well in the end. So I bought the sides from Blue Nile, the center from Mark, and had a jeweler in LA make the custom setting for me.
~~Congrats!! I must say that I absolutely love the look of a three stone cushion! That ring blows me away!!!! Did you have any trouble finding two squarish cushions that matched the center stone?