The plea for Tab came across in a message on Facebook.

It was Sept. 27, and Anne White saw a post from a neighbor telling her their local grocery store in Cincinnati had been stripped of the diet soda, last popular in the 1980s and now a cult favorite.

“I drank my last one a few days ago and I’m suffering from withdrawal,” the neighbor wrote. “Where are you guys getting it?”

Ms. White, 56, had 10 cans stashed in a cupboard and agreed to leave them on the porch. The next morning, two were gone. Since then, Ms. White has not been able to find Tab anywhere in town. She reserved a few cases online at a Target near Wilmington, N.C. But when she went to buy them, it was sold out.

“A friend brought me three cases from Atlanta,” she said. Those are sure to go fast too.

“It’s a little bit sad, isn’t it?” Ms. White said.