I, too, come from a smaller chapter on my campus. This fall we'll have about 70 members while the other two have 95 or 100. My first suggestion would be to buy "I Heart Recruitment" from the people at phiredup.com. We've passed it around our chapter and it's been really helpful! It has a lot of exercises to get your members excited for recruitment - they might seem kind of hokey, but they really do get people motivated!
One of the BIG points they emphasize is personal connections. PNMs wgo go into recruitment wanting a certain group almost always have a personal connection to that group. Make friends with PNMs before recruitment starts (if that's allowed), or at least try to get some face time by helping with freshman move-in/orientation, or more events if your recruitment is deferred. In the recruitment room, focus on conversation skills, not glitz or refreshments. Those things are nice, but no one joins a sorority for the decorations or the rice krispie treats. They join because they felt a personal connection with the sisters.
I agree with what someone said above - for COB, have every sister bring someone. If every single girl in your sorority could recruit just one PNM, you could double your size - or if that would send you above quota or chapter total, you'll at least have a really big pool to choose from when you decide who to bid. And don't just tell your sisters, "Give me a name and I'll send the girl an invite." Have the sister PERSONALLY deliver the invite, then PERSONALLY meet up with the girl to walk them to the event. Many PNMs are intimidated by the thought of walking into a room of sorority women they don't know, so having someone they know to walk them in and introduce them around can make a big difference. It may also get them motivated to go to the event even if they're on the fence or aren't super-excited about it - and if your sisters are strong recruiters, they'll be able to change that PNM's mind
