Here you go-

Western Mountaineering

1025 S. Fifth Street
San Jose, CA 95112
408-287-8944

Phone:

408.287.9844

Usually, they'd like it if you go through a store, but being backcountry.com, it's a little difficult so you can probably just go through them to get an overfill. Give them a call and ask!

Hope this helps!

used the above info to call them (number is not generally published i was told) and visit store back in Nov '12; took 3 bags in to get the overfill-got a detailed personalised tour of their operations; helpful and friendly service, told me that generally people just send in the items with instructions on what they want, rarely get visitors for service more than a couple time a year. process was complete in about an hour; overfill pricing is bag dependent and ranged from $30 to $80 (bag design/stitching was more intensive labor-wise to access)