A holistic Vet gave me an essential oil to use for flea treatment. It is a blend by Young Living Essential Oils (only this brand is safe for application on pets or humans) of: Lemongrass, rosemary, niaouli, lavender, myrtle, and citronella. Do a search for young living purification and you'll find it.
Anyway, I put 1-2 drops into a tiny bowl and add about 1 tbl veggie oil to it to dilute the concentration. Then I take an eye-dropper and put a few drops on the back of Max's neck. The fleas are gone within a week of putting a drop or two on he back of his neck once every few days.
But like with everything, check with your holistic vet before trying alternative stuff. This mix will also kill fur mites.
You could also try buying a bunch of fresh rosemary and lemongrass, simmering it in a pot of water for 30 min with a few tablespoons of cloves added until it is well steeped, and then bathing your bunny in this every few days once it is cooled off. Or put in a spray bottle and spray onto fur until mites are gone.
They repel bugs and fleas can't stand it, also anti-parasitic so kills mites.
Just be sure to not get the steeped herb water or oil near their eyes and mouth.