I found a workaround of sorts. It takes more steps, though.
First, open the Search & Outline sidebar, and enter your search term. Then, click Select and All. Next, on the floating control bar, select … > Export to other Mindmap Notebook. You will be prompted for the name of a new notebook. Finally, open the new notebook that you just created. It will contain only the notecards you found in the search, linked to the PDF. You can now export this.