Too bad you are not up in the SF Bay Area, Keeble & Shuchat has some. I just picked up some 100-ISO cartridges, and the guy asked if I wanted any 400-ISO cartidges and pulled out a box of at least 24.
If you can't find any, call or email K&S.
If you call, ask for the darkroom dept. Be patient, things are a little confusing right now, they are moving the darkroom dept from one building to another, and stuff is in boxes to be moved to the other building. So the guy answering the phone may in the other building from where the cartridges are.