I have Ovation Hearing hearing aids (internet company). They set the hearing aids to the results of my hearing test. They work great! Cost of aids was good - right and left BOOST MODEL aids for $550 total... but replacement domes are expensive. I would like to get small open hearing aid domes and tubes "just in case" but don't know of any generic or other brand I can buy. Does anyone have any knowledge in this area? Thank you in advance