The paper "Move Over, Roger Maris: Breaking Baseball's Most Famous Record," Journal of Statistics Education, 1998, can be obtained here.
In 2001 Barry Bonds broke Mark McGwire's season home run record. I have put together a data set that adds Bonds' 2001 game-by-game results to McGwire's and Sosa's 1998 results. A comma-delimited version of the data can be obtained here. An Excel spreadsheet of the data can be obtained here. A description of the variables in this file can be found at the link to the paper given above (the variables referring to Bonds are the last nine variables in the data set, and have the same format as those for McGwire and Sosa).