Thanks for your questions“How can I find a part time job as a piano player in a restaurant or cafe in the US?”  I think this questions restaurant or cafe is very important for all like yours.
Here I’m trying to give your answers in brief.

International students who come to the U.S are generally restricted from working part time off- campus. In fact, F1 students cannot work part time off-campus in their first year of study. After one year of study, you can apply for OPT if you would like to work part time during the period of your study. If your OPT is not approved, you cannot work part-time off campus. And even if your part-time OPT is approved, it will reduce the time of your full-time OPT by half amount of your part-time work. Also, unless the subject your study is music, you cannot work in a music-related field.

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