Ambergris is reputedly illegal to possess (or trade) in the United States[1], so depending on the authors&#x27; location--which appears to be Pennsylvania--they might not live in an area where they can gain access to it, and certainly not legally so.<p>The talk page on the Wikipedia entry[2] for ambergris is of interest, particularly regarding the legality, and appears to suggest that the Marine Mammal Protection Act[3] provides precedence even prior to the Endangered Species Act (which prohibits trading parts or products of endangered animals, as I understand it).<p>I can&#x27;t speak as to why they&#x27;d omit marrow, because I&#x27;d imagine most butchers would be willing to part with bones fairly readily (Google suggests this is the case, particularly for some ethnic cuisines). I&#x27;ve never cooked with it nor sought it out, so I can only hazard a guess.<p>[1] <a href="http:&#x2F;&#x2F;www.bloomberg.com&#x2F;bw&#x2F;magazine&#x2F;ambergris-treasure-of-the-deep-01122012.html#p2" rel="nofollow">http:&#x2F;&#x2F;www.bloomberg.com&#x2F;bw&#x2F;magazine&#x2F;ambergris-treasure-of-t...</a><p>[2] <a href="https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;Talk%3AAmbergris#Illegal_to_buy.2Fsell_in_USA....Is_this_certain.3F" rel="nofollow">https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;Talk%3AAmbergris#Illegal_to_bu...</a><p>[3] <a href="https:&#x2F;&#x2F;www.law.cornell.edu&#x2F;cfr&#x2F;text&#x2F;50&#x2F;216.13" rel="nofollow">https:&#x2F;&#x2F;www.law.cornell.edu&#x2F;cfr&#x2F;text&#x2F;50&#x2F;216.13</a>