From Sourceforge Downloads

Download the file from the sourceforge site and put it under the plugins directory of your maven installation

Maven Auto Download

Run the following maven command:

maven plugin:download -DartifactId=maven-eclipse-checkstyle-plugin -DgroupId=maven -Dversion=0.9.1 
	              -Dmaven.repo.remote=http://mvn-eclipse-chk.sourceforge.net