Klokard,
They might have been referring to Carl Childress's "Baseball Rule Differences" (BRD) which you can acquire here:
http://shop.officiating.com/x/product/brd2006
Carl first published this in 1982 and updated it every season up until 2007. (Don't know why he didn't this past season.)
It's actually much more than "just the differences" - great all-around reference for anyone who wants to understand the rules & interpretations better.
JM