Now that that is out of the way, here's a couple more tips for working with agency signed models.
Email every agency in your city and surrounding cities.
I'm serious. Every, single, one.
When I first wanted to shoot with signed models, I emailed every agency I could find in hopes that just one would respond. Because here's the thing – Agents are constantly receiving inquiries from photographers. They're inboxes are full of client emails, modeling inquiries, new model submissions, photographer inquiries, etc. and they don't have time to respond to everything. You have to be willing to be persistent and capable of handling rejection. Don't send one email and then never try again.
I emailed Dragonfly (who I now shoot for on a regular basis) a handful of times before ever hearing back. AND THAT'S TOTALLY OKAY. It didn't mean my portfolio sucked or that they hated me – it just meant they got busy and had more important things to do that day. As a creative, you HAVE to be able to brush yourself off and get back on the horse.
Campbell Agency told me no when I first inquired about working with their models. They told me I needed more tear sheets (aka published work), and to email them again when my portfolio was more established. Guess what? I emailed them again a year later and was approved to shoot with their models. Be persistent!
Once you've connected with an agency (and you've proved yourself valuable to them) they will begin setting you up with their models. During your slow months, you can email the agent with you're available dates and ask them to do a "push" for you. This means they would send out your open dates to their local models and see if anyone is interested in booking with you. This doesn't always guarantee work, but it's a good way to remind the agency you want to work with them and to keep your name in the model's minds.