Have you looked at the Arduino micro computers, that cost anything from £2 upwards, you can programme them to flash LEDs randomly and run off any thing from 5v to 20v.
I have programmed one to illuminate a card shop that came free with a model railway mag, on the ground floor it has two white LEDs that are on all the time, on the second floor there are three LEDs red, blue & green, each of them flashes at random flicker rates and brightness to represent TV flicker and on the top floor I have 1 LED that comes on and off every 30 seconds.
The Arduino mini I use is only about the size of the top of you thumb and runs of a simple 9v battery.
Programming the Arduino is simple using free software and a USB port, all you need is a soldering iron and you imagination.
Here is a link to the Arduino website to give you an idea what I'm on about
My work bench is starting to look like Portsmouth Naval Dockyard.