If you want true random, then many CPUs/SoCs have environment based TRNGs. The SoC used in the rPi can emit half a million random bits per second (that passed the statistical tests I threw them through), and many Intel chips have an RNG in them now (though I don't know if it is as easy to access in userland as the rPi's is).
If you need more than your current CPU provides then you could chain a bunch of them together, or pick a good PRNG for your main source and simply reseed that on a regular basis with the output of your TRNG.
There are some concerns with generators like those in the rPi as they are not documented, so you have no way of knowing exactly how good they are or if the manufacturer has somehow arranged for there to be some predictability - but if you are that paranoid you need to be building your own generator from scratch anyway!
If you need more than your current CPU provides then you could chain a bunch of them together, or pick a good PRNG for your main source and simply reseed that on a regular basis with the output of your TRNG.
There are some concerns with generators like those in the rPi as they are not documented, so you have no way of knowing exactly how good they are or if the manufacturer has somehow arranged for there to be some predictability - but if you are that paranoid you need to be building your own generator from scratch anyway!