Steve,
Like Momotaro food Izeki is very hard to get it. When Izeki comes in it usually sells out as it comes in. Momotaro food we'll never get your hands on it.
If your looking for summer food I would try Hi-Silk...There are 2 Makers of Silk food:
Hi-Silk - Kawaguchi Shoten
Silk Power - Ogata
Both foods are good for growth while not to spoil the Shiroji. For Ogata Silk Power I would contact Eastern Nishikigoi (
enkoi.com) they are the West Coast Agents and they should be getting a shipment in soon. For Hi-Silk I would contact Japan Koi Online (
japankoionline.com) they have medium pellets availible still and are getting a shipment in soon.
As, for Izeki and Momotaro good luck finding it. Your better off goin to Japan and "hand carrying it in".