Internet searches do not yield a result with a Thai address or Thai contact details for IMG, so I doubt they have an office in Thailand. If that's the case, then IMG is not regulated by the OIC and local brokers are prohibited from selling IMG's products.
In the past, some brokers would sell offshore insurance products here, but to avoid having an auditable link to an offshore insurer their clients were often directed to pay the insurer directly. I think some of the brokers that did this in the past have stopped. I don't know if any still do, but it is possible.