This is CPU Frequency Scaling Monitor applet icons I created for Humanity icon theme.
This version is with greyscale fill.
To use it, copy icons to you /usr/share/pixmaps/cpufreq-applet/ directory.
To do it in terminal, cd to extracted icons and do
sudo cp cpufreq-* /usr/share/pixmaps/cpufreq-applet/
Updated version available at