Don't virtually all PCs have a hardware RNG these days? Although it's rarely used as such. It's the integrated audio system.
Rack up the gain on the microphone input and you'll hear noise generated by the switching of other electronic systems in the box. (Even better if a mic is connected and you pick up external noises). It shouldn't be hard to generate a fairly random number from a second's worth of samples thereof. It may not be good enough for crypto on its own, but XORing it with a "good" random number cannot make it any less good.