Our son sent us a SIM card for a different service so we canceled one of our Republic Wireless phones. I was told I need an unlock code and the Moto G3 (from Republic) will work with the new carrier. Where can I get an unlock code?
While the phone are not subsidy locked (what you were referencing), the Moto G 3rd Gen is purpose built from the manufacturer to work on our unique system. For this reason, they will not work on any other carrier. There is no way to get the phone to work in the way you are seeking.
Republic Moto G 3rd has a custom ROM to handel Republic WiFi first Hybrid VOIP/Cell and can not be used on any other carrier