It appears that Bicycle NSW has something to do with the installation of bike lockers at train stations - although I don't know about the ongoing management and maintenance of them.
A quick bit of googling discovered that the CEO of Bicycle NSW is Alex Unwin, so I sent him this email:
The bike lockers at North Strathfield station have been heavily defaced with graffiti (as you can see from the attached photos). The area around there is a graffiti hot spot, so it is not surprising that they have been hit - but how do we go about getting them cleaned up?
I got a response in 17 minutes:
Thanks for the heads up - we'll get onto the MOT re this.