Turns out there is nothing (as of writing) that I can find online that will integrate Netbeans and Redmine.
Last night I got tired of waiting so began working on a plugin for myself. This was challenging for a couple of reasons, not least that I haven't looked at Java in years.
Hopefully later on tonight I will have a link up to my Github with version 0.1
Update: Please see the GitHub repo I created that does basic integration between Netbeans IDE and Redmine.