Hi,
There are several makers on the board who do resin or fiberglass helmet kits. Depending on what material they use to cast them,
they can range anywhere from white to beige to several shades of gray.
But these are all unpainted kits that will require prep and painting.
Some makers you can look up are: Animefan, Wasteland, Asok, Bobamaker, or Darth Voorhees. There might be a couple more
that I'm forgetting (sorry!)
It's unusual that anyone would be selling a completed white helmet.