Greetings
4.2mm is really close to a #8 tap diameter and .35mm pitch is really close to 72tpi. Victor machinery has #8-72 for $11.50. If the part that uses this tap is plastic then the threads are likely molded and the #8 tap may work. I have been successful locating non metric taps for molded threads because they are a "sloppier" than cut threads. Good luck.