Theoretically any insurer. Insurers carrying on business in Australia must be authorised by, or registered with, the Australian Prudential Regulation Authority (APRA). Check the quotes you receive are from authorised or registered insurers. If you use an insurance broker, agent or other distributor then they must have an Australian Financial Services Licence (AFSL) issued by the Australian Securities and Investments Commission. In practice, some general insurers will provide more attractive or comprehensive strata insurance products.