Hmmm, rare but not modern. How about:
Ariel, April, Aphra, Anika, Anne, Alexis, Adele, Amberley, Ariadne, Asha, Alba
Bronte, Bree, Bay, Belinda, Bridget, Bronwen, Bryony
Clarice, Celest, Cherry, Cecile, Calista, Celia, Cynthia, Calliope, Carmen, Coral
Darina, Davina, Doria, Dorian, Deloris, Dana, Dina, Darrell, Diana, Delphi
Erica, Eilidh, Evadne, Elisaveta, Elowen, Elspeth
Faye, Fleur, Fern, Fabia, Fenella, Felicia, Fiona
Gloria, Giselle, Guinevere, Griselda, Geraldine
Henrietta, Honor, Hester, Harmony, Honey
Ida, Irena, Isolde, Isadora, Iona, Ingrid, Irma, Inez
Jessamy, Jocasta, Jacinta, Juliana, Joelle, June, July, Jessa, Jerica
Kirsten, Karensa, Katinka, Kathleen, Keziah
Liandra, Leonie, Lavinia, Leona, Larissa, Lorelai, Lois, Lettice, Lesley, Liberty
Miranda, Millicent, Melisande, Morven, Meryl, Melody, Mirabelle, Marina, Maeve
Neriah, Noelle, Noa, Nadia, Nadine
Octavia, Ondine, Odette, Opal
Primrose, Patience, Pandora, Prunella, Phyllis, Phyllida, Posy, Paloma
Queenie
Rosina, Rowena, Ramona, Rita, Ruth, Reagan, Rosemary, Rosalind, Rivkah
Serenity, Saffron, Sorrel, Sylvia, Susannah, Samaris, Sapphire, Sephora
Trinity, Tamara, Tamsin, Tanya, Tegan, Taryn, Tansy, Thalia, Tiffany, Tamika
Ursula, Una, Ulrika
Verity, Vanessa, Vashti, Veda, Vera, Viola, Velvet
Winona, Willa, Wanda
Xanthippe, Xanthe
Ysanne, Yvette, Yvonne, Yolanda
Zeryn, Zillah, Zelda, Zipporah
I think boys names are harder. The majority of uncommon boys names are quite modern, I think. Maybe:
Alistair, Anthony, Axel, Angus, Abraham
Benedict, Bradley, Boaz
Cole, Crispin, Christian, Caspian, Cassian
Damien, Dominic, Dustin, Declan
Evan, Ellis, Edwin, Edgar, Edmund, Enoch
Francis, Ferdi, Fraser
Gregory, Gareth, Gaius
Huw, Horatio
Ian, Ivor, Ivan, Igor
Jeremy, Jonah, Joel, Jonty, Joaquin, Jesse
Kit, Kenneth, Kevin, Kester
Linus, Ludo, Leolin, Lester, Lachlan
Malachi, Monty, Martin, Moses
Noel, Norman
Otis, Orson
Percy, Perry, Paul, Philip, Patrick
Quentin
Rupert, Robert, Richard, Ronald, Rowan
Solomon, Scott
Tavish, Titus
Ulysses
Vincent
Wilbur
Xavier
Zebediah, Zephaniah, Zecaraih