Or perhaps take the lyrics from your favorite song and convert the letters to their respective number rank in the alphabet. Then heads for even and tails for odd numbers.
When poker players need a random source (for instance, deciding when to bluff) they can look at the current or previous tabled cards (or their own cards).
> unless you know the starting position of the die, mass, size, air currents, force of throw, on and on. With perfect data, you could predict the outcome.
This is what Einstein believed, but he was wrong (quote about God doesn't play dice). Physics uses the Copenhagen Interpretation, which means that we have probability waves until we measure and the wave collapses. You may have also heard of the Heisenberg Uncertainty Principle (read: "There is a resolution to what we can measure").
The fact is that you can't know all your conditions. That's why we say things are random. Because there is a probability distribution to all these constraints (even if we had a device that could measure with "infinite" precision. The problem is that the universe itself hides information from us.
There's great sources for true random numbers. White noise (in atmospheric data), particle decays, particle motion (yes, even particle motion), etc.
Tldr: There's a lot of random stuff.