There is no textbook for the course, but there is plenty of material available to help you help you learn the subject matter.
The first reference you should check are the lecture slides, which are available in both PDF and PowerPoint formats. A redacted version of the slides is passed out in each class and a complete version is posted online after the lecture. http://csg.csail.mit.edu/6.375/handouts.html
In addition you may find the it useful to check out BSV by Example , a book from Bluespec Inc which helps you learn BSV by discussing running small, complete examples.
Periodically, you may need to consult the Bluespec SystemVerilog Reference Manual ( reference-guide.pdf). This is very useful for finding libraries and understanding the language syntax, but is not meant to be a tutorial.
For help with running the compiler and other various tools associated with the language you will want to consult the Bluespec SystemVerilog Users guide (http://www.bluespec.com/forum/download.php?id=107 or bluespec.com -> Resources ->Wiki -> BSV Documentation -> User Guide).
All of the above Bluespec documents are also available in the local installation of Bluespec at $BLUESPECDIR/../doc/BSV/. In general, you should look for resources on Bluespec Inc's website. www.bluespec.com