There are several things to consider on how that ballast apparatus is designed, which components it contains. In the most basic case you just need a basic ballast for plasma tubes of same voltage and wattage and number of tubes.
However the wording of your request makes me rather advise to have that luminaire inspected/repaired by an electrician.
Such coil getting hot as such is normal. Quite some share of the power of the tube in addion is released as heat in that coil. Installing an electronic power supply instead is an alternative, as it yields some benefits. My own experiences though showed the longevity of such may be two decades, whereas coils run seemingly forever. (The energy saved by such electronic device then must be related to their price/longevity.)
