Are there any available stencils available for download to help create process flows or network diagrams?
Take a look to this extension:
http://extensions.libreoffice.org/extension-center/smart
LibreOffice templates link:
http://templates.libreoffice.org/template-center
Too late to help the original query, but maybe of help for others following. In addition to the ones above, if the “network diagrams” are physical communications networks, then a further extension containing shape galleries may also help: http://extensions.libreoffice.org/extension-center/vrt-network-equipment/
A sample of the shapes that are included are here: http://www.vrt.com.au/downloads/vrt-network-equipment