Rhodium

Start by consulting a Chemist locally that can help.

You will need a rhodium salt to do this. Rhodium chloride, sulfate, nitrate, etc. If you cannot locate a supplier, then the next step would be to make it yourself. Dissolve rhodium in an acid and you will have your salt solution. Once the metal is dissolved, neutralize the solution and that can then be used for plating. The most common way to plate is using electrolysis. Basically you connect the metal to be plated to the negative end of a battery, the sacrificial metal to the positive end and immerse both into the plating solution.