RTI Act requires every public authority to provide information under the Act.
Section 2(h) of the Act defines public authority to include -
(d) (ii) non-Government organization substantially financed [...] by funds provided by the appropriate Government.
Section 2(a) of the Act defines "appropriate Government" to means in relation to a public authority which is established, constituted, owned, controlled or substantially financed by funds provided directly or indirectly—
(i) by the Central Government or the Union territory administration, the Central Government;
(ii) by the State Government, the State Government.
Thus, if the association referred by you is substantially financed by the State or Central Government, it is a public authority within the meaning of the Act and accordingly liable to provide information under the Act.
If association referred by you is not a public authority within the meaning of the Act, then also you may get information by making application under the act to the Registrar of Societies. However, registrar can provide you those informaton which can be accessed by him under Societies Registration Act or any other law.