Obtaining or commissioning prints/posters of non-mainstream paintings?

[Jo]

For many years now, I've searched fruitlessly for prints of several
paintings, and I've concluded that unless one's taste runs strictly to
Klimt or Van Gogh, searching for specific reproductions is an exercise
in frustration.

Does anyone know if there is an industry or individuals that
specialise in creating reproductions of less-common paintings?

I don't even know what the process is for reproduction, but I'm
assuming it involves photographing the original?

I'm specifically looking for repros of:

Rush Hour, New York (Max Weber, National Gallery, D.C.)
Bather (Max Weber, Hirshhorn, D.C.)
Zirchow VII (Lyonel Feininger, National Gallery, D.C.)
Sea-Dancer (Gino Severini, Guggenheim)

Any hints/clues appreciated.