All of the Alpha characters I can think of--Bernard, Helmholtz, Mustapha Mond, the DHC, Henry Foster--are men. And none of the female characters seem to be Alphas. Lenina is probably a Beta. Linda is stated to be a Beta-Minus. Fanny Crowne is probably also a Beta or Beta-Minus since she works in the Fertilizing Room and it seems like all the technicians at the Hatchery are Betas (Linda worked in the Bottling Room).
There's some minor circumstantial evidence against the existence of female Alphas; at the beginning of Chapter 4 it says "The lift was crowded with men from the Alpha Changing Rooms", as if the Alpha Changing Rooms are all-male. But the door Lenina opens towards the start of Chapter 3 just says "Girls' Dressing-Room", not "Beta Girls' Dressing-Room". I'm not entirely convinced by this, though.
Do we know if female Alphas exist? Can we infer their existence or non-existence from evidence in the book?