Sea cucumber is called namako – I think they eat this raw in Japan.
However, the salted entrails are called: Konowata and this is really what you should be looking for in Japan as along with uni (sea urchin) and karasumi (EDIT: DRIED mullet roe) it is one of the ‘top three’ delicacies of Japanese cuisine.
(Like the top three gardens, or the top three sights, this doesn’t mean they really are the best – but I’m glad you’re going to give it a try!)
I've seen Konowata in depachika (department store food halls) but I don't know where else you could find it - I'm sure some of the other FTers (with bigger budgets for meals than I have) can recommend a place.
EDIT: just found this link with some more info:
http://www.japantimes.co.jp/cgi-bin/...20021110rl.htm
(I've just learnt why karasumi reminds me so much of Spanish Hueva - one of the most popular presents I take to Japan with me)
Missed your last question:
Konowata tastes NOTHING like chicken (my partner's grandmother fed me some)
(but I don't know what fresh namako is like)