Robert Fliegel was craving a Hydrox. The 52-year-old computer consultant says he always liked the way the chocolate sandwich cookie, which he found crisper than Oreos, "stood up to the milk" when dunked. But Mr. Fliegel, who used to be able to devour an entire package of the crème-filled biscuits in a sitting, couldn't find them in any stores near his East Stroudsburg, Pa., home. Only when he went online a few months ago to try to order some did he learn the truth: Hydrox is dead. In 2003, without warning or announcement, Kellogg Co. killed off the cookie --...