I know the turns ratio formula and such, but I have no idea where to get the magnetic core for it. Any ideas?
The iron core that you see in other transformers, or relays, solenoids, and things like that are the magnetic core that you are asking about. It is simply the powered iron material that has been shaped for use in a transformer, or other type of coil, or the thin metal plates of iron that are used in other transformers. They are all called magnetic core because they help to channel or focus magnetic waves that are made when an electrical current passes through the windings that have been wound around them. One point to keep in mind, not all coils are going to have any kind of core in them. You'll find this to be true in some radio coils.
you can buy them from companies that make cores. Or you can find an old transformer of the right power rating, and use the core from that. .
