Of course there could be hardware products that would meet an independent auditability criteria. It would require a completely open hardware design where the only thing that is done in hardware is a noise diode, and the minimal circuitry to convert the analog signal into a digital one. A quick google search reveraled something like this that could perhaps be used as a basis of such an implementation:
Add a simple USB interface so it can be plugged into a laptop or a server, but the key point is that it's a open hardware design, using basic commodity parts whose operation can be easily verified.
Then what we do in open source software is all of the hard work of analyzing the raw output of the hardware circuit, to make sure it hasn't failed, and then all of the whitening using AES, etc. Alternatively, we could take the unwhitened output and just feed it into /dev/random (since the /dev/[u]random entropy pools will take care of doing the whitening for us).