The source code of the rpc-jira-plugin is absent from the source distribution, even though it is a bundled plugin:

jclark@BLUETONGUE /e/source_distros
$ cd atlassian-jira-5.1.7-source/

jclark@BLUETONGUE /e/source_distros/atlassian-jira-5.1.7-source
$ find . -name rpc-jira-plugin -print

jclark@BLUETONGUE /e/source_distros/atlassian-jira-5.1.7-source
$

The JIRA RPC Plugin's source code is normally accessible via https://svn.atlassian.com/svn/public/atlassian/rpc-jira-plugin, but is currently restricted due to some release issues.

This means that currently there is no way for external developers to view this code, which is problematic because the plugin source also contains the example Java SOAP Client that we link to on the JIRA SOAP tutorial - https://developer.atlassian.com/display/JIRADEV/Creating+a+JIRA+SOAP+Client

Exposing the full, canonical repo for the plugin is probably overkill - people generally just need to see the code as it stands in a particular JIRA version.