I doubt a LaTeX version is available of the old volumes. You can get vector (draft) PDFs of parts of the newly released 4th volumes though, since Knuth released the drafts himself.
What's interesting is that a draft version of Concrete Mathematics is available (by doing a simple Google search), and it looks very similar to the final edition. I'm not sure why the publisher wouldn't just release the finalized PDF as the draft looks pretty good on my iPad.
You doubt that a LaTeX version exists, or that one is made available for publication? It is my understanding that part of the reason for writing TeX in the first place, was for use in personal publications...?
What's interesting is that a draft version of Concrete Mathematics is available (by doing a simple Google search), and it looks very similar to the final edition. I'm not sure why the publisher wouldn't just release the finalized PDF as the draft looks pretty good on my iPad.