Since Calico coloration results from X-inactivation, which requires two X chromosomes, but these are males which normally have one X chromosome. Thus, the 1/3000 must be XXY males (Klinefelter's syndrome), since these can have X-inactivation.
Work Step by Step
To get to this answer, the key is that Calico coloration requires X-inactivation, which, in turn, requires two X-chromsomes. Then, it is simply a matter of finding a way that a male can have two X chromosomes.