There are no male myconids, and no female myconids, technically. Them all seemingly having a male voice is just the direction Larian went with the limited VA we currently have. They communicate telepathically via spores, so I imagine they could sound like whatever they wish to, even an ambiguous type of voice, however I don't really see how it matters all too much. I especially don't see why it would matter for one or two of the mushrooms to have grown with non-functioning breasts.
There's already fanart of female myconids and general mushroom people, so if you just want to see what they'd look like if they had almost visible sexual organs, then they're just an image search away.