Safety magazine, having been in a similar situation (a few years ago ) we overcame the problem in 2 steps.
We had indeed the pressure of management not to have printed or electronic messages discussing safety-related issues ( in our case severe incidents ) for the same reasons as you described.
The First solution used was to have briefings sessions at regular intervals , informing and discussing those issues.
That cost a lot of money ( scheduling and taking shift working staff off duty to attend briefings, staff involved in giving them , etc..)
Then came the ICAO Human factorgs Annex which, among other things describe the " just culture" , whereas people are invited , and even rewarded to report safety issues. Introducing Just culture was relatively easy on paper, but took a lot of convincing , especially towards middle management.
We are now trying to implement some form of it since one year, quite successfully so far I must say.
Internal Paper bulletins are used now , distributed individually, those are far better than electronic information ( e-mails ) whose further dessimination is far easier and uncontrolable.
We also de-identify the reports ( date/hour call signs, names, even exact locations, etc) to make sure in case a bulletin is leaked to the Press .( which has not hapenned so far ).
Of course an ATC Center is not as " juicy" as and airline for the Press, but if you de-identify sufficently , and use a lot of acronyms ( which we have plenty of in our business ) there in fact little sensational news for them.
Good luck, and do not give up, perseverance is the key.
ATC W.