In the United States, today, "two dozen police officers" is the best choice.
Fifty years ago, "Two dozen policemen" would have been the natural choice. If asked "does that mean none of them were women," the answer would have been "the word 'policemen' includes both genders."
I feel uneasy about "two dozen police." It doesn't seem quite right to me. It is using a count ("two dozen") with an uncountable noun ("police!") Strictly, "the police" refers to an entire organization. "Hundreds of police" seems fine, and it turns up in a Google News search of newspaper stories. So I think "hundreds of police" is acceptable, and so is "dozens of police." I don't think "three police" would be correct.