A locksmith can do it. You should be able to use aftermarket fobs too, but the originals from discount dealers are relatively affordable in the US. My problem was that when the fob was linked to my car it created an annoying error display (with original fob too) before start up that you had to clear. When he removed it, the error disappeared. (I had found my spare key at that point!) I don't know if it related to the fact that the my fob was not "factory". It had an OEM Mazda case (the old style, this was for a 2018) probably sourced from the Chinese market for its China built CX-5s based on the approvals on the back. The circuit board was an upcharge because it supposedly was OEM (it had a Mitsubishi logo). So I think it was my fob rather than the software used by the locksmith. I bought it from a Chinese guy in Australia where dealers wanted USD 500. The locksmith used the standard made in China pad to add the fob. It was programmed to support the late model CX-9. I observed the entire process with him. I forgot the brand name, but they only cost a few hundred bucks. There is a guy from England on Pinterest who shows how he programs an aftermarket fob for a CX-5 using this pad. I think it's called XTool.
