I'm in the Friend Safari and I keep encountering Barbaracle but every time it's a female.
I checked Serebii and it says there is a 50-50 chance of male or female but I tried for more than half an hour (I'm not exaggerating!) and nothing but females.
So my question is: Is their a gender lock on Friend Safari which is preventing me from getting a male Barbaracle?
You are just really unlucky. I kept encountering the same Pokémon over and over for about 10 minutes. Just be patient and you will find a Male Barbaracle. Also, I caught a Male Barbaracle in the FS myself.