The phrase "a specific reason why" is correct and usable in written English.
It can be used when you want to inquire about the particular justification or explanation for something.
Example: "Can you provide a specific reason why you chose this course of action?"
Alternatives: "a particular reason for" or "a clear explanation for".
Asked for a specific reason why McKiernan was being removed, Gates said: "Nothing went wrong and there was nothing specific".
There is usually a specific reason why they don't like heights, so we can talk it through.
"There's a specific reason why it has been difficult to play in Giants Stadium -- grass has been the No. 1 issue," said the federation spokesman, Jim Moorhouse.
Like most of the similar pieces in other papers it also referenced my low opinion of the tabloid press as a specific reason why I should be loathed.
Silas would not give a specific reason why Coleman was losing the title, saying, "Do you have to ask why?" last Wednesday.
Asked if there is a specific reason why the singer and guitarist will never, ever, ever, ever, ever, ever, ever, ever reconcile, the publicist said: "You'd have to ask Morrissey that.
For the HERG recordings, is there any specific reason why the external concentration of KCl was only 2.5 mM?
There is a very specific reason why Israel Rank has been shrouded in reticence and unspoken embarrassment.
There is, or there has been, a very specific reason why Jesús Navas has failed up to now to follow up the scintillating form he displayed as a youth for Spain's Under 21s.
Once a leading financial centre is established and the City has had centuries of experience its position tends to be self-reinforcing, since businesses and talent are attracted to the cluster like bees to pollen.There is a more specific reason why London's economy may prove resilient this time: the impact of the £9 billion that is being spent on preparations to host the Olympic games in 2012.
As it turns out, there was a very specific reason why this failed to pass.
