MakoMike, while I believe you have found O Toro available in some of the high end Japanese restaurants you know, I have never seen it in NY or other cities where I have visited And I have eaten in some really fancy places like "Iron Chef" Morimoto's place in lower Manhattan. What I have seen on some menus is a premium cut of Tuna referred to as "Belly Tuna" which was superior to the standard offerings. However none matched the O Toro I recall from Tokyo. If you can suggest a place in the NY metro or LI area that does have O Toro please let me know.
IMHO, Roccus is quite right about Uni (sea urchin). It can be terrific or really terrible depending upon the freshness and preparation. Harkening back to my comment about "Gas Station Sushi" for the folks who have been to Japan, there is a fish snack sold in the 7/11 style convenience stores there known as dried Cuttlefish. It was a sort of fish jerky. Man you had to have a lot of tolerance to eat that stuff. Personally I thought that belonged in the category I refer to as "Cat Food"!