Do you know how to use google? Enter: mid 50s bathroom tile

Jim: you beat me to the posting. I was going to say the same thing. Or enter: mid-century tiles

Description of mid-century:

Mid-Century historic trim tiles matched tile, pink, green, blue, and yellow tile for bathrooms and kitchens from the 1920's, 1930's ,1940's, and 1950's.

I think just by using Google you do get a lot of false leads and information.

Heath Ceramics makes a number of dimentional tiles that are mid century

https://www.heathceramics.com/collections/dimensional

As does Subway Ceramics/Heritage Tile in their Atomic Tile line (designed by Saul Bass, a graphic designer who did movie title design for Hitchcock among others)

https://subwaytile.com/samples/atomic-tile.html?p=1

And Fireclay makes a number of "Mid century" shapes.

https://www.fireclaytile.com/tile/patterns/

However, quite honestly the most common large field tile of the mid century would have been 4.25 x 4.25 or 6 x 6 square; and 4" hex.

The common smaller tiles would have been porcelain mosaics in 2x2 square, 1x1 square, 1x2 rectangular. and a mix of these in a pinwheel pattern or "text" pattern, and 2x2 hex. For these just look at someplace like Daltile at Semi Gloss or Keystones. There was also very small 1/2" square tile too.

These would have been much more common than the shaped tile, for most houses of the period excepting relatively high end installations. (In my area architects seemed to favor all over treatments of 1x1, 2x2 or 1x2 porcelain.

I save pictures of original baths and kitchens from real estate and I just came across this one in an intact house from 1959

westseattle,,,go to RetroRenovation. they specialize in those time capsule bathroom tiles. tons of pics, how to's, links, etc.

Try Pam Kueber's Retro Renovation. It has all sorts of source guides for remodelers of MCM homes. Try this page, for example.

Here is a collection from Tesselle: https://tesselle.com/collections/mid-century-modern-cement-tiles

https://tesselle.com/collections/ipanema-cement-tiles