I would assume the reporters read the case files (when they are public) themselves.
Criminal files are always public. Reporters generally do read the files themselves if they are going to write about them. It's not always practical for reporters to go through every single criminal case that ever gets filed. So they depend, sometimes, on the police to tell them about newsworthy cases. But once that happens, the reporters read the file. And police don't normally try to hide newsworthy cases from the reporters.
I can't imagine either the police or the news media deliberately conspiring to hush up cases of male rape. Why would they? What would be the motive? If this were ever to happen, there'd be a Pulitzer in it for anybody who uncovered it.
The only explanations that make sense to me are 1) it doesn't happen that often 2) when it does happen, the victims, if they're living, often don't report it, 3) when they do report it, it doesn't get a lot of attention. Even rapes of women only get a lot of media attention when the case is already high profile because the victim mysteriously disappeared, or because the rapist is related to the Kennedys, or something like that.