Try the Confederate Constitution itself.
Article 1 Sec 9
(I) The importation of negroes of the African race from any foreign country other than the slaveholding States or Territories of the United States of America, is hereby forbidden; and Congress is required to pass such laws as shall effectually prevent the same.
(2) Congress shall also have power to prohibit the introduction of slaves from any State not a member of, or Territory not belonging to, this Confederacy.
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I've read that and nothing in that document indicates that slavery would have died out in a few years. In fact, it guaranteed slave imports from those U.S. states that allowed slavery and which provided quite a few slaves to the deep south. And there are other sections, like Section IX, which guarantee that individual Confederate states could not ban slavery within their borders and that the government could not pass any laws that impaired slave ownership. Or Article III which mandated that any territory the Confederacy acquired would be slave territory. So it doesn't look like the Confederate Constitution was trying to limit slavery, exactly the opposite.
But I would still be interested in hearing about the history books you spoke of which predicted that slavery would have ended within a few years regardless of whether the South had left or not.