Most of the defensive drills are designed for use with the IPSC target.
These targets are available from many different suppliers, usually in lots of 25-50.
A rough substitute for the IPSC A-zone is a sheet of 8.5 x 11" paper. This is the same height and just slightly wider than the A-zone. Most of these drills can be practiced with a sheet of paper on a cardboard backing if you don't have IPSC targets.
Variations: Some agencies tape 3x5 cards in the center of a silhouette for many of these drills, and only count those hits. The theory is that in an armed encounter your group sizes will widen involuntarily, so practicing with a smaller-than-life stop zone is better training.
Please note that I intend to expand this section with a set of downloadable targets. I am currently in the process of acquiring printable targets from around the web for access at this site. Please check back soon for an update.