There is a new repo in the flot org on Github called "flot-plugins". I have added the plugins we have built here at National Instruments and a couple of contributions from other folks to get it started. The build of this repo creates a single NPM package for all the plugins. Anyone is welcome to contribute - at this point the main guidelines are simply to write tests, docs and examples for each plugin added. At some point I plan to add a Github page with demos for each plugin from the examples.
Comments and feedback are also welcome.