I have not heard of Mobile number hunting being offered as a service. This function would be up to the SIM provider, and is not a function of the Gateway or 3CX, but is doesn't hurt to ask if they can set this up for you.
Each SIM is an individual phone number. If you can change the destination of call forward busy, which would normally go to the mobile voicemail, to the next SIM instead, then if the first were busy, the next number would ring. This could be repeated for each SIM. However...the provider may only allow one call to be forwarded at a time. So, if the mobile were on a call, a second had come in, was forwarded to the next SIM, and was still active, the third caller may receive a busy signal.