You have your best shot with themed anthologies because you already know what the editors are looking for.
Flame Tree Publishing: Accepting Submissions for Three Anthologies
Flame Tree Publishing is an established press that is distributed by Hachette UK, which is also now a shareholder. (You can learn more about the company and their imprints here.) They occasionally have calls for themed anthologies. Currently, are accepting submissions for three fiction anthologies, part of their new Myths, Gods & Immortals series. “Each book brings back to life a classic mythological or folkloric figure, with completely new stories alongside the original tales. New and emerging writers from open submissions, reveal hidden themes, casting fresh perspectives on well-known stories, alongside specially commissioned text on the origins and the cultural background of the mythology. The first three books will focus respectively on Odin, Anansi and Medusa.”
— Odin: “Everyone knows about Odin, the All-father, the one-eyed, all-seeing, powerful King of the Gods, presiding over his great hall Valhalla, surveying the nine realms and the billions of souls. He bears the pain of Ragnarok, the joy of travelling in disguise through Midgard and shapeshifting in the dusk joins his ravens in their flights across the mythic landscape. Featuring new stories from open submissions this enthralling book reveals the larger-than-life stories of Odin and his kin, their adventures in the ancient and the modern world, with the gods, the giants, the valkyrie and the creatures of the epic Norse literature. Stories submitted for consideration need to explore new angles to the character: have him follow alternative paths, present different viewpoints, imagine new futures, or perhaps pursue story lines that are hinted at in the original tales.” Details here.
— Anansi: “Anansi is at once a creator god, a trickster folk hero, a wily spider and a heroic symbol of resistance. From his origins in West African folklore, to his lauded status in Jamaica, Anansi is a versatile immortal whose many stories reflect the early world of his origins, and the potential for re-imagination. Sometimes dark and chilling, occasionally light-hearted, but always lively and clever, Anansi appears in the lives of everyday folk, pricks the pomposity of the mighty and in this collection of new stories, appears in the modern and the ancient world, a symbol still of individuality and resilience, adapting to City life, with the undertow of ancient lore ever-present. Stories submitted for consideration need to explore new angles to the character: have him follow alternative paths, present different viewpoints, imagine new futures, or perhaps pursue story lines that are hinted at in the original tales.” Details here.
— Medusa: “Variously described as a fiend, a monster, a charming seductress who was felled by the righteous might of Perseus, son of Zeus, Medusa is perhaps the most misunderstood of mythological women. Described by male historians and epic writers such as Virgil and Ovid there are many aspects of her imagined life which find resonance in the struggles of the outsider, the cursed and those used in the service of another’s vision of the world around them. This fascinating collection brings together new stories and ancient origins, offering a wider perspective on the whole life of the powerful, wonderful Medusa. Stories submitted for consideration need to explore new angles to the character: have her follow alternative paths, present different viewpoints, counter the patriarchal narrative and male gaze, or perhaps pursue story lines that are hinted at in the original tales.” Details here.
They will also accept reprints for all of these calls. They also say, “Story length is most likely to be successful at 3,000-4,000 words, but we will still read stories slightly outside this range.” The series will be published in hardcover.
They will pay $0.08/word for original stories, and $0.06/word for reprints.