The requirement for steam testing comes from the recent EN285 guidance, and other agencies are starting to adopt that guidance as well. There are test kits available to perform the testing using one simple aparatus. We bought a kit and paid for someone to train our QC/Micro personnel to perform the testing. It wasn’t super difficult.
When you state that you cannot do this kind of test for an autoclave with a dedicated generator. Why is this? Is there not a port available to do the testing? If there is not a port available, I would expect the agency to simply ask you to add a port in the line between the steam generator and the autoclave chamber. I think a “T” and a valve would be all your need. I’m not sure if there a configurations of the piping that are required. You might want to work with the autoclave manufacturer, and the testing kit manufacturer to figure out the best location/configuration for the “T” and valve (or some other sampling fixture).
A google search for EN285 and test kit came up with a few good results and articles.
Here is one (I have no association with this company)