An RTL-SDR [0] commodity hardware device paired with rtl-entropy [1] seems to have great potential for filling this need.  It has some nice write-ups [2][3][4] and ongoing development.<p>0: <a href="http:&#x2F;&#x2F;www.rtl-sdr.com" rel="nofollow">http:&#x2F;&#x2F;www.rtl-sdr.com</a><p>1: <a href="https:&#x2F;&#x2F;github.com&#x2F;pwarren&#x2F;rtl-entropy" rel="nofollow">https:&#x2F;&#x2F;github.com&#x2F;pwarren&#x2F;rtl-entropy</a><p>2: <a href="http:&#x2F;&#x2F;blog.cros13.net&#x2F;2014&#x2F;08&#x2F;cheap-entropy-using-your-rtl-sdr-as.html" rel="nofollow">http:&#x2F;&#x2F;blog.cros13.net&#x2F;2014&#x2F;08&#x2F;cheap-entropy-using-your-rtl-...</a><p>3: <a href="https:&#x2F;&#x2F;pthree.org&#x2F;2015&#x2F;06&#x2F;16&#x2F;hardware-rng-through-an-rtl-sdr-dongle&#x2F;" rel="nofollow">https:&#x2F;&#x2F;pthree.org&#x2F;2015&#x2F;06&#x2F;16&#x2F;hardware-rng-through-an-rtl-sd...</a><p>4: <a href="http:&#x2F;&#x2F;blog.krisk.org&#x2F;2013&#x2F;12&#x2F;high-quality-entropy.html" rel="nofollow">http:&#x2F;&#x2F;blog.krisk.org&#x2F;2013&#x2F;12&#x2F;high-quality-entropy.html</a>