searching for shiro maguro, sometimes aka "super white tuna," hopefully to be found somewhere not terribly upscale. its unusually smooth -- like a slab of ivory on the plate -- with a delicate lemony flavor (mmm.) and it was around here a few years ago, though i don't remember the exact spot, and is super-popular in chicago. but i haven't been able to find it yet at tomoe, ebisu, etc. anytime in the recent months. help?