Try the John Bridge Tile forum:

https://www.johnbridge.com/

They would NOT have had “thin” grout lines in 1915. 1/16th? Nope. You need to do more research as to what is historically appropriate. https://www.ceramictilefoundation.org/find-certified-tile-installers

The photo I added to my question didn't come up in this post. It shows exactly what I'm trying to replicate and it's less than 1/16".

You're telling me that I'm wrong and I need to do more research... Would you mind just telling me what you're alluding to, or where this "research" is located?

1/16" is the minimum allowed according to the TCNA (Tile Council of North America)

If you wanted anything less I would walk away from the project. As should any tile setter.

Will you find someone to do it? Sure. You will even find some who will butt them with no joint. Expect to pay the consequences. There is a reason this detail exists.

Try to find local historical preservation groups and ask homeowners of similar style houses about their contractors. In our local area, I know of a few homeowners who are very detail oriented and concerned with historically appropriate projects. Then start asking and if someone tells you it is out of their geographic area or not their speciality, ask them if they know anyone to contact. It might take several conversations before you get some names but eventually you will come across people who are interested in your type of project.

Start by finding some completed projects which interest you and work backwards to find contractors and material sources. Local historical societies, historic homes tours, and high end realtors and specialist shops might provide some contacts. Municiaplities with historic districts probably have some person or committee that reviews projects. Old house junkies are passionate about their subject and if they have some time, most are happy to provide assistance with contacts and suppliers.