Giving Zakat For Building Masjid
As you have stated, Ghamidi sahab maintains in the light of Quran verse 60:9 that zakat can be spent فِي سَبِيلِ اللَّهِ (fi sabilillah):for serving Islam and for the welfare of the citizens . However, if the institution that you want to give your zakat to has clearly stated that they do not want to accept zakat then the only two options remain as a ) educate the management of your institution about the law of zakat; or b ) spend your zakat in another prescribed manner. For reference, here’s a comprehensive resource on zakat including prescribed heads in the light of the Quran: Discussion 46733