Also, another fun list would be female characters from the Jeeves and Wooster books. This would include:
Honoria (the root of Nora)
Myrtle (:P, but that is just my response)
Isabel (obvious problems wit recent popularity)
Lavender (But I am not sure if this is a male or female!)
I've always liked Isadora but, not fond of the meaning. My husband is in love with Evelyn but, it's quite popular. Margo is cute but, unfortunately I have a cousin who has that name. And surprisingly my husband and I wanted to use Maxine but, it was used as a name for my dad's pet crow back in the day! Can you believe that?! Genevieve is beautiful but, I agree that it's too similar to Vivienne. Amelia is my husband's best friend daughter's name! Hazel, Coco, Stella, Lola, Charlotte, and are also friend's children names. I like Flora and Florence but, I hate the nickname Flo. Rose is my aunt's name and my daughter's middle name. And Margaret is my other aunt's name. We actually were going to use Grace for Vivienne but, decided it against it. Frances is also a family name. I do like it but, find it unisex and not very feminine. Jacqueline I have a not so good association and Beatrice is a friend's name. Whew!
Thankfully you ladies have tons of name that aren't in use! So there's still hope for lol.
Sorry for the repeats. I just searched "famous flappers" and here are some that i got...
Mlle (no idea how to say that one. No it isn't a typo.)
Roxanne might be too similar to Vivienne...the other option would be Roxana, but I don't know how "flapper" that is.
Irene doesn't strike me as overtly "flapper," but it was definitely popular in the '20s, and I like how it sounds with Vivienne.
Doris...My initial impression was that it sounded dated, but now I adore it and the nickname Dot.
Good luck with your search!