I would direct you to the Old House forum for a wider pool of opinions and possibilities. This paper, to me, looks post 1940 rather than earlier and it's probably roller printed or block printed with heavy ink rather than hand painted.

There are companies that do recreate wallpaper patterns but they usually have at least a repeat or section of the whole pattern, and the process is time-consuming and expensive. They would also do this in the expectation of being able to produce and sell the pattern as a part of their regular offering.

Adelphi Paper Hangings is one American company who reproduces historical patterns but they tend to concentrate on the Federal to pre-Civil War period with a few offerings of unusual patterns after that period.

You could look at Carter and Co. Mt Diablo Handprints for historical papers of much more recent vintage, but I don't know that I've seen anything like this in their offerings. On the Retrorenovation website there are some links to resources of actual vintage papers from the 20th century. For a powder room you may be able to get enough vintage paper for the whole room.

I would try posting on the decorating forum.

Take a look at the third wallpaper down -- it's similar to your photo and apparently currently available. It's hard to tell the scale, however.

Here is a link that might be useful: C'est magnifique wallpaper

There's also this one.

Here is a link that might be useful: Paris skyline mural

The best places I have found to research old wall paper is

Historic Wallpaper Specialties and Spoonflower

Just google them.