How can I access Maven Artifact POM using Maven's Java API?

I am attempting to retrieve the entire dependency tree and their poms starting at the root of the project. I am starting with a POM already existing in my file system, but I'm not sure how to retrieve the dependency poms from the repository.

I am using the following code to access the dependency list. From the list I have all the information on the artifacts. I'm just not sure how to access the repository.

FileReader reader = null;
Model model = null;
MavenXpp3Reader mavenreader = new MavenXpp3Reader();

File pomfile = new File("pom.xml");

model.setPomFile(pomfile);
MavenProject project = new MavenProject(model);

List<Dependency> deps = project.getDependencies();

// Get dependency details
for (Dependency d: deps) {          
    System.out.print(d.getArtifactId());
    System.out.print(":");
    System.out.println(d.getVersion()); 
}