On Donald E. Knuth's website, Knuth states that "new and updated printings of Volumes A, B, and C became available in April, 2012", but I cannot seem to find these anywhere. Knuth describes these "spiffy new printings" as "fresh versions that are essentially perfect", being "significantly better in hundreds of small ways" compared with the Millennium Boxed Set. The InformIT website does not seem to list any of them; in fact, InformIT does not seem to list any books in Computers & Typesetting series published more recently than 2000. Perhaps they are published by another publisher?
Where and how can I obtain the "spiffy new printings"?
N.B. questions similar to this have been asked but closed as off-topic; this is odd to me since there is a tag called {books}, "for questions which deal with books about TeX, LaTeX and other topics of this site". Therefore this would seem to be very on-topic to me, and is certainly pertinent to my sincere and pertinent interest in learning TeX. I reviewed What topics can I ask about here? and What types of questions should I avoid asking? and do not feel that my question is off-topic.
Best Answer
See update at end.
This is rather more complicated than it appears.
The new printings involve the hardcover editions of the Computers & Typesetting volumes. The situation as of October 2012 was described in my TUGboat column, and I won't go into all the details here.
These are new printings, not new editions, so most booksellers don't distinguish, and it's generally not clear whether what is being sold is the new printing or an old one. To quote from my column,
It's likely that the new printings are the ones in common circulation now, but it never hurts to be careful. Besides, TUG does get a small commission on books sold through this offer, and that goes to help support CTAN and other TeX-related endeavours.
update (as of 20 January 2021)
As long as someone has been nice enough to give this an upvote, I may as well provide the latest information.
2021 is a review year (all reports had to be turned in by 31 December 2020, and a lot of people worked very hard to find something that hadn't already been reported). Don Knuth has reviewed them, and accepted some of them (I don't know the details), so there will be updates to books. Discussions are going on with the publisher, and paper copies will be produced. (The details of that aren't final yet either.)
At the moment, the publisher's website has the C&T books shown as not currently available, at best back ordered. When more information is available, it will be posted on the TUG website, and it is expected that some special consideration will be made for TUG members, at least continuation of the current discount. Please stay tuned.
Update as of 22 September 2021
The new printings are now listed at https://www.informit.com/promotions/computers-typesetting-jubilee-editions-142316 (Thanks to Svend Tveskæg for the pointer.)
A 40% discount on the printed books or ebooks is available to TUG members until the end of 2021; see http://tug.org/books/#pearsonaffil for instructions.