Mark, I'm also a part time photographer and started shooting art nudes a couple years ago. Some of the model/photographer sites such as One Model Place and Model Mayhem are good places to start. Overall, I've had better luck with Model Mayhem, However, if you don't have many people images, you might want to start with OMP as your portfolio there doesn't have to focus on images of people.
I've also had a little luck with myspace and more luck with craigslist. With both Model Mayhem and OMP, expect to have to contact a lot of models before you get one. The response rate can be very poor, so stick with it. It's unlike you'll get any models to start with unless you are willing to pay. $30-50/hour with a two hour minimum guarantee, will probably set you up with a few amateur models. More experienced models are more likely to be $75/hour and up.
Once you've established yourself and have a solid portfolio of images, it's easier for you to negotiate.
I think it also helps to have webpage to refer models to that shows you are serious and tasteful, as well as give copies of your usage rights agreement and model release.
Mine: www.artphotosforsale.com/models
Best of luck.