The phrase "not particularly forthcoming" is correct and usable in written English.
It is typically used to describe someone who is not openly sharing information or being cooperative. Example: The politician was asked about his plans for the future, but he was not particularly forthcoming with details.
He was all business, and not particularly forthcoming in response to philosophical questions.
In caring so much about the fate of this particular bunch, people have been given the opportunity to honour miners, to show them the respect that they deserve and that in many parts of the world is not particularly forthcoming in the cut-throat world of heavy industry.
Almost without exception, African American voters proved to be enormously cordial and hospitable, though not particularly forthcoming.
Franklin himself isn't particularly forthcoming on the subject.
It's not a surprise then that those who dabble in the Afro-Carribean religion's white magic aren't particularly forthcoming about it.
Strahan has not been particularly forthcoming about the drop.
But he doubled down on his questions about Clinton's health, saying her spokespeople have not been "particularly forthcoming".
Fingers are collectively crossed that state involvement will lead to constructive movement towards equality in funding - that this isn't merely a political chess move meant to challenge the Mayor, who hasn't been particularly forthcoming, or forthcoming at all about the absolute lack of transparency on how and why there's been a 40 plus percent differential for years.
Monáe hadn't been particularly forthcoming about her sexuality in the past.
Alas, Google hasn't been particularly forthcoming with information about its AI projects.
The commission hasn't been particularly forthcoming with members of the media, either.
