Quantum effects are the source of this "True Randomness". E.g. the Heisenberg Uncertanity Principle says that your dice thrower can't exactly define both impulse and location of its throwing arm. (Reading up on pop-sci quantum physics can be scary - the predictability and stability of our world seems to be no more than a great feat of statistics.)
There are - as mentioned in other replies - appliances that turn quantum effects into observable random number generators. There are algorithms to "extract" the randomness of any stream of data. There are test algorithms to check if a stream of data "behaves" like a random stream.
OTOH you can argue rather successfully that "random" is a man-made concept, i.e. something that isn't integral part of the objective world, but our limit of understanding (though the uncertainty principle is considered to be not just an observer effect).
When someone asks for any random number generator, the counter question should be: for what application? In the context of this discussion: who do you need to fool? Pseudo vs. True are just generation mechanisms, not fundamental opposites.
In that sense, chaotic beahvior is often "random enough" for most purposes, and can be cretaed with few degrees of freedom already.