This was fun, as it came as a total accident. I was walking by the front garden, and knocked past some drooping chive plants. I stopped as many tiny black seeds scattered themselves all over the pathway. Prolific little buggers, those chives must be, if they procreate like that!
Harvesting chive seeds is ridiculously easy to do. Holding the chive flower, cut it at the base of the flower. Take the flower and shake it over a surface which you can gather the seeds from after. You can make this even easier, by instead of taking the flower with it, you can simply shake the flower heads out on a surface which you can collect from after. Saving chive is so easy. I'm surprised that i don't eat more of these delicious little creatures!