More detail from The New York Times:
Mr. Penn met with the Colombians in his role as chief executive of Burson-Marsteller, a global public relations firm. He has refused to sever his ties to the company, which also represented Countrywide Financial, the nation’s largest mortgage lender, and through a subsidiary represented Blackwater Worldwide, the military contractor blamed for numerous civilian deaths in Iraq.
The Japan Foundation is one avenue of foreign influence.FEC information on campaign contributions and foreign nationals.
There are restrictions on PAC activity by US subsidiaries of foreign corporations (see link above). But there are plenty of foreign-connected PACs.
An example of direct government lobbying: the Canadian embassy.
APCO issued a response to the Silverstein story.