Recreating a local repository from a currently existing wordpress.org repo..which I own

Use this URL format for checkout (if using TortoiseSVN, just right click and do checkout from Explorer):

http://plugins.svn.wordpress.org/your-plugin-name

You will need to use your username/password for WordPress (the account used to publish the plugin) to do any commits.

Command line instructions are available direct from WordPress here: https://wordpress.org/plugins/about/svn/