Anyone out there can you give any info on where I can purchase an on board camera in a van for my layout.

Tricky for N, but there certainly have been small cube cameras etc. sat on flat wagons. Either recording to micro SD card or even transmitting to a TV

I experimented with one a few years ago, it was ok but once you've seen one cab-ride around your layout you've seen 'em all

A google search should find you some results.  For example:

https://www.hookstonemodels.co.uk/n-gauge-cameras

Look up ESP32cam, they are very small and ok for recording idlf not ideal for streaming. PiCam using raspberry pi is better but bulkier so probably no good for you.

Have a read through this thread to get some tips

https://www.ngaugeforum.co.uk/SMFN/index.php?msg=510533

The SQ11 camera is cheap as chips and the micro SD card you'd need to buy probably costs more

https://tinyurl.com/bddxvj4f