We have introduced a feature that allows you to download a list of IP address information for a given "Threat" that you can then use to issue takedown notices.
You can find this feature by going to Reports, click on the Senders tab and underneath that click on the Threats tab. 

You can multi-select "Threats" and use the Download IP List button underneath the table to download a CSV file containing all the IP address informtion.

NOTE: IPs resolving to a known service will not be generated.