Where do I find the GSD file for the DP/DP coupler?

There is no separate GSD file for the DP/DP coupler. The DP/DP coupler can be selected directly in the hardware configurator of the Simatic Manager or TIA-Portal under the Siemens order number "6ES7 158-0AD01-0XA0 DP/DP coupler, edition 2" and inserted into the project.