I know that 3pt diamonds come in huge lots and that they are not likely to be graded to the same extent larger diamonds are, but does anybody ever actually take the time to grade D If 3pt diamonds. I would be interested to know.
There was a program in one of our large retail accounts that offered Flawless diamonds in D/E/F color range in the size you mentioned. I had an opportunity to take a look at several of them and they seemed carefully graded. It is possible to do it, just not economically popular.
The stones can be obtained by going through large lots of better small diamonds for the very highest end of the lot. There is a premium price to be paid for the upper end and also for the added labor of sorting the stones so carefully.