You can find small rabbits, a rabbit breeder is your best bet there but online suppliers would have them. You could also rotate with other prey such as chicken or quail. I absolutely would not be feeding two prey items or jumbo/colossal rats, that's not healthy in the least, very fatty and hard on their systems. I'd stick to a large every 2-3 weeks at max. You need to let her work through an entire digestion cycle before stuffing her with more food, your current feeding schedule is going to leave you with an extremely overweight boa.