How to convince my parents to get me a 2nd rabbit?

[IBeBekah]

I think it could benefit your rabbit, too, to have a companion.
Rabbits like companions.
And like you said, if you get the same sex rabbit, babies wouldn't be a problem, but fighting -might-.
Rabbits can become territorial.
*Can*.
Tell him something along the lines of, if you can't get a companion for your current rabbit, she'll become depressed from social starvation.
(Lol)
Although this isn't entirely true, it's worth a try. o.o
Otherwise, your dad may have his own reason for not wanting to have a second rabbit. Such as, more waste, more responsibility, more noise, etc.
Good luck!