Illustration by Ernst Deutsch-Dryden from a 1927 Die Dame.
(source: MAK)
Illustration of beachwear including Schiaparelli trousers, sweater, jacket and sandals, and Hermès scarf and cocktail shaker, in the July 1929 French Vogue.
(source: Gallica)
Dogs and beach pajamas on the Venetian Lido (dog on the right is called "Yanky Dude"), from the November 1927 French Vogue.
(source: Gallica)
Photo from the July 1927 Moderne Welt.
(source: Österreichische Nationalbibliothek)
Frau D.P. in a sunbath in a Carinthian village and Mrs. Ordway wearing an atlas pattern robe, from the July 1927 Moderne Welt.
(source: Österreichische Nationalbibliothek)
Beach fashions, illustrated by Harriet Meserole in the July 1924 issue of French Vogue.
(source: Gallica)
Fashion illustration by Eleanor Johnson of Marie Prevost modeling a jacquard knit swimsuit, “Cat’s Pajamas” bathing bag, and floral print beach coat in the June 1926 issue of Photoplay.
(source: archive.org)
Illustration (I believe by Helen Dryden) for an article about beachwear titled "Summer Life Cradled by the Waves” in the July 15, 1921 issue of French Vogue.
(source: Gallica)