The only BMT material I have is posted on the BMT-Lines.com site. It includes track and signal maps of the Astoria and Flushing Lines
http://bmt-lines.com/wp-content/uploads/2010/11/astoria-flushing.pdf
as well as a complete Southern Division electrical map
http://bmt-lines.com/wp-content/uploads/2010/11/bmtsoutherndiv.jpg
There are a few more links you might find interesting too: