Some things to consider, external input even if not totally random can increase randomness, including but not limited to human interaction of a button press duration for example...
Other options include the use of a thermistor, photo diode, photo resistor, or a simple variable resistor circuit based on audio detection levels can all help generate randomness if integrated into say a timer or oscillator circuit to shift speed...
If you use a micro, may I advise you to a few locations of the EEPROM to store multiple increasing and decreasing values that change with each power up and/or change based on the duration the micro is powered up or a routine is activated and/or are based on and external reference, an analog read of a floating pin actually produces a pretty random value in many instances... Use these ever changing values to seed the internal random routines, using your own equation to derive at the seed, use another equation to generate some new numbers to put in the EEPROM for the next cycle... Doing this for all intents and purposes is random...