The c model for this core is a product of IP core generation in Vivado. The c model delivered is parameterizable rather than specific to the configuration described by the GUI fields, so all that is required to generate the C model zip file is to generate any configuration of the core. The c model zip may then be found in the cmodel directory of the instance generated (after running Generate Output Product in Vivado) <project_name>/<project_name>.gen/sources_1/ip/<instance name>/cmodel/.
E.g. For the FFT IP (v9.1) in a project called myproj and with the default configuration of the FFT IP (v9.1), the lin64 C model can be found in myproj/myproj.gen/sources_1/ip/xfft_0/cmodel/xfft_v9_1_bitacc_cmodel_lin64.zip
The C-model is available if the IP is generated when added as a design source. If IP is added as a part of block design, the c-model is not available.
Unzip the FFT C model zip file. This produces the directory structure and files shown in Table: Files for the FFT Bit-Accurate C Model .