The phrase "has been interested for" is correct and usable in written English.
It can be used to indicate that something has been an interest of yours for a certain period of time. For example, "I have been interested in photography for five years now."
A plan to bring in McDonald's fell through in the 1990's, and Wendy's has been interested for at least three years.
But the RSC director, Greg Doran, said he has been interested for years in the best way to convey the immediacy of theatre through the medium of film.
"Bernie has been interested for some time now in making Zen more accessible in our times and culture, relevant and down-to-earth, and he felt that 'Lebowski' did that big-time".
The deal is notable for Facebook, which has been interested for some time in bringing live sports content to its network.
The UK Department for Environment, Food and Rural Affairs DEFRARA) has been interested for some time in the use of DNA-based tests to aid law enforcement and to help combat this illegal trade.
Our research group has been interested for many years in the molecular mechanisms controlling the cell division cycle of budding yeast.
Republicans have been interested for years; Richard Nixon opened the new Grand Ole Opry in 1974 and George Bush attended the industry's awards show in 1991.
The word "empathy" — a rendering of the German Einfühlung, "feeling into" — is only a century old, but people have been interested for a long time in the moral implications of feeling our way into the lives of others.
Scientists have been interested for years in the observation that ratios of finger lengths differ in men and women.
Moore's Law is an area that Kleiner Perkins has been interested in for at least the past few years.
There has been interest for some years now in the development of duplex treatments involving plasma nitriding coupled with the deposition of a hard coating.
