Retro graphic designs are always doing well on t-shirts and other POD (Print on Demand) products. This Free Retro Microphone T-shirt Design is no exception. It is offered by DERAJ and can be downloaded for free. An EPS and PNG file are included.
It comes with a commercial licence, so you can upload it directly to your favourite POD marketplace, like Teepublic, Printful, Printify or Etsy.