U.S. branch is located in California. I found this on Namco's website:
About Namco Hometek Inc.
Namco Hometek Inc. is the U.S. consumer division of Namco Limited, a Tokyo-based world leader in the high-tech entertainment industry. Based in Santa Clara, CA, Namco Hometek Inc. is an award-winning video games publisher for next generation game consoles.
And then searched on Namco in Santa Clara using switchboard.com and found:
Namco Hometek Inc
4555 Great America Pkwy
Santa Clara, CA 95054-1243
Phone: (408) 235-2000
EDIT:
Also searched on mapquest.com and found their holding company location, which explains the part San Jose listed on games:
Namco Holding Corp
2055 Junction Ave, San Jose, CA
408-383-3900