O'Reilly & Associates specializes in UNIX books. Their "UNIX In A Nutshell" has been updated for SVR4 and Solaris 2.0. Get their catalog by calling 800-998-9938 (1-707-829-0515) 7AM to 5PM PST.
SunSoft Press carries books specific to Solaris 2. Look for the inset with your End User Media Kit that lists the most relevant ones.
Prentice-Hall has reprints of much of the AT&T documentation. I'm not sure how much of this you need - a lot of the same material is in the Answerbook (see above).