Javiar, the blue ones with "tropical fish" with graphics all over the box typically come from Florida. They'd be far too expsensive to have shipped empty to Portland though. On the west coast, each wholesale typically has his or hers done just like Piero said, via their own supplier. Unfortunalty I don't have any names of the top of my head, sorry.
If you don't want it printed, US Foam is a good supplier. I'm not sure if they're national though, their local for me.