From what you are saying I think I would be tempted to leave the 2 boys together for now and not try to get one of them a wife. That will probably be adding fuel to the fire (more to fight about).

Mounting is also a dominance behavior so it sounds like your one bun is trying to reinforce to the other that he is the boss.

I'm puzzled about why they never fought prior to enlarging their cage. I guess the fighting could be a combination of the one bunny insisting he is the boss as well as having the increased territory. I would not make the cage smaller. All manufactured rabbit cages are too small for rabbits, no matter what size the cage is..... think about it: you have a very active animal(s), that naturally want to run, skip, hop, do binkies and play constantly. Any confinement is too small for them. In an ideal home, they wouldn't be caged at all....unfortunately that is not realistic in most homes. Rather than enlarge the cage again, if it isn't too late, I would suggest you build or purchase an exercise pen and, if possible, have it attached to the sides of the cage so that it extends away from the cage and gives them a "backyard" to play in. In the pet stores they are sold as puppy pens, usually octagon in shape. I've seen nice, heavy pens which I recommend. Some stores sell flimsy light-weight wire pens which are probably more for hamsters and guinea pigs; they don't work well for buns. I think the smallest heavy duty puppy pen I've seen gives them 6 feet of space while the fencing is 24 inches high. There are 4-5 larger sized of pens in addition to this smallest one which go up in area and height. Many rescue groups and the House Rabbit Society prefer these pens to cages as they do give the buns more room and are usually less expensive than the largest cage that pet stores have for sale. Plus they are portable. I think combining the cage with the puppy pen is the best of both worlds: rabbits tend to feel safer in their cages and will often retreat to them when they have been allowed out in a room, yet they have the extra space to move around and be safe in.

If you decide to look for a female I would first check to see if there are any rabbit rescue groups in your area. You could also try your local humane society or animal shelter. Unfortunately with Easter just having past there will soon be a lot of unwanted rabbits that were given as impulse holiday gifts that are no longer wanted. The last place to get a rabbit from is a pet store or breeder since there is already such a significant problem with homeless rabbits. Rabbits are being abandoned or put down at humane socieites/shelters at an unprecendented rate and where do all these excess, unwanted rabbits come from???? Impulse buyers, breeders and pet stores.

I hope my comments help you some. I would go back to the HRS website and read up again on caging, bonding and introductions though. Good luck.