Simulations I have created since 2001 were generated with EJS. However, simulations shown under JDK1.0.2 simulations category were not created with EJS. For example, this one. That is the reason why you dod not find the xml source.
It should not be difficult to create a simulation like this one with EJS. Try to play with it, I will try to help you if you have problem.  But you need to let me know what you would like to do and upload your source code.