I think this is Callistemon subulatus however I can’t be 100% sure because it was dug from a garden and the owners had no idea what species it was.
It was dug in 2012 so I have now been the proud owner for six years. It has a great feature for bonsai in that the leaves are quite needle like and small in comparison to other bottlebrush. It also flowers well and the flowers are small (again in comparison to other bottlebrush) and so more in keeping with the size of the bonsai.
This year it had a larger number of flowers, around 30 so I am pleased. However the majority at the back so here is a photo of what was previously the front but that was changed to the current view a couple of years ago.
I have made a new pot for this bonsai and when it stops raining I will put it in its new home and post a photo later.