Check out this one on Etsy. The provide a measurement for each piece in this collection except for the subway tile soap dish! But, I bet you can contact them for more info.

https://www.ebay.com/itm/404886071174?itmmeta=01HXSPE2P35CA12VEK1GT4X5P2&hash=item5e45172786:g:2NMAAOSwAE9mHzBX&itmprp=enc%3AAQAJAAAA8MD%2BPEw%2F12ZrYCRuLf13DvjaUX10jT1BpOPa%2FhWEModro%2F%2BH0Ln3mZkTfebWpFIfrkfqLstRdUNQ8SWAzprWjSPXyjVmb9d%2FH%2FIas5cS19tYf9Mp863U9zUjKDd5Fnmkczo%2F7MgHIbz%2BBCZZaCvnfw1crF05OfcwJEFVqWGW2jpEKzFv9rlDHSrhwo%2FpR8vdLZGpol1FXPEIJX6%2FWxh5Tb%2Bn5fNvEYQHUzO3T5T9jigpK7xZ7i6KuMbbCmWovUwzhC%2BlWRh7EnJ0PDoZyMIOCrjCGfg63HTqd%2Fv5PbwfG4B8bYr3cnzScoGq5QZng3zDZw%3D%3D%7Ctkp%3ABk9SR5qruLbuYw

Thank u!

Try the period bath supply co. Or Historic Houseparts. I didn't see a soap dish, but I did see a cup holder that looked like it would work.

My Dad sold me on black nail polish as a temporary fix to fill in white drill holes on a black ceramic tile floor. Maybe until you get .your new soap dish in you could use some nail polish to cover the white hole. Probably not needed, but boy was it fun painting a floor with nail polish. I felt like a four year old making mischief.

You could have one fabricated out of Nocturne (solid black) Corian with a gloss finish. It wouldn't be cheap, but it would function and fit perfectly.

Call Mission Tile West in Los Angeles. They sell and manufacture period appropriate tiles for old Spanish, MCM and Craftsman style homes in CA.