The Raspberry Pi has a hardware random number generator. Quick testing shows it can provide sufficient entropy to read from /dev/random at around 35kB/s.

• Build the the bcm2708-rng kernel driver (required on at least raspbmc):

  sudo su -
  apt-get install build-essential bc gcc make
  cd /tmp
  wget http://www.mirrorservice.org/sites/raspbmc.com/downloads/bin/kernel/linux-headers-latest.deb.gz
  mkdir x
  dpkg-deb -x linux-headers-latest.deb.gz x
  mv -v x/usr/src/linux-headers-$(uname -r)/Module.symvers /usr/src
  cd /usr/src
  gKernel=$(uname -r | sed 's/[0-9]*$/y/')
  wget --no-check-certificate https://github.com/raspberrypi/linux/archive/rpi-$gKernel.tar.gz
  tar xzf rpi-*.tar.gz
  mv linux-rpi-*y rpi-linux
  cd rpi-linux/
  make mrproper
  zcat /proc/config.gz > .config
  sed -i 's/CONFIG_CROSS_COMPILE.*/CONFIG_CROSS_COMPILE=""/' .config
  apt-get install ncurses-dev
  make menuconfig
  # Enable HW_RANDOM and HW_RANDOM_BCM2708
  cp /usr/src/Module.symvers .
  make modules SUBDIRS=drivers/char/hw_random/
  modprobe hwrng_register
  insmod drivers/char/hw_random/rng-core.ko
  insmod drivers/char/hw_random/bcm2708-rng.ko
  mkdir -p /lib/modules/3.12.31/kernel/drivers/char/hw_random/
  cp drivers/char/hw_random/bcm2708-rng.ko /lib/modules/3.12.31/kernel/drivers/char/hw_random/

• Install and start rngd to populate the local's system entropy pool from the hardware rng:

  sudo apt-get install rng-tools
  sudo bash -c 'echo "bcm2708-rng" >> /etc/modules'
  initctl start rngd

• Install NetRNG on both clients and the server:

  sudo apt-get install git python-virtualenv python-dev
  git clone https://github.com/infincia/NetRNG.git
  sudo mv NetRNG /opt
  cd /opt/NetRNG/
  git fetch --tags origin
  git checkout -b v0.1 v0.1
  virtualenv /opt/NetRNG/env
  source /opt/NetRNG/env/bin/activate
  pip install -r /opt/NetRNG/requirements.txt
  sudo cp netrng.conf.upstart /etc/init/netrng.conf 
  sudo cp netrng.conf.sample /etc/netrng.conf 

• Start the NetRNG server on the Raspberry Pi:

  sudo initctl start netrng

• Install and run the NetRNG client on each network machine:

  sudo vim /etc/netrng.conf
  # Set mode = client, and the server IP address
  sudo initctl start netrng

• Verify it's working:

  # Whenever the pool drops to 128 it should very quickly be refilled
  watch -n 0.1 cat /proc/sys/kernel/random/entropy_avail
  # For extra fun, try this both with and without netrng running:
  cat /dev/random | pv -bart > /dev/null
  # For me this measures 13KB/s with netrng running
  # but only small numbers of B/s rapidly dropping towards zero with netrng stopped

For systems that use systemd instead of upstart, use the following service definition:

/etc/systemd/system/netrng.service

[Unit]
Description=NetRNG Entropy Client
After=syslog.target
 
[Service]
Type=simple
ExecStart=/opt/NetRNG/env/bin/python /opt/NetRNG/netrng.py
User=root
 
[Install]
WantedBy=multi-user.target

• Currently the random data is provided over the network in cleartext which is not ideal. Stunnel or some kind of VPN would fix that, alternatively patching the netrng source code to use an encrypted socket connection.
• A puppet module to manage the installation and configuration of client/server parts