Just by watching commercials and looking in magazines at ads and editorials you see that Plus Size models Do get work. I also see Plus size models in hair magazines as well. Enjoy this story on ABCnews about Plus Size models and the modeling business.
For fashion Plus Size modeling there ARE requirements usually you still have to be taller, 5'7" or taller. A size 12, 14, 16 is prefered. But for Commercial print modeling, and commercial print modeling agencies, which is not so fashion related, but more commercial modeling and modeling lifestyle products based, there is NOT a height requirement.
For Plus size models and petite models it is more about being proportioned, and photographing proportioned.
So I would look at some catalogs and ads that involve plus size models and try to create images that look like them. include products into your photos.
Show that you can MODEL something, alot of girls think modeling is just about themselves but modeling is more about "can you actually model that product, make it look great and sellable?" Whether it is clothing or an iPod.
Instead of looking for a PLUS SIZE Modeling Agency I would actually look for commercial print agencies, or modeling agencies that have a plus size division. Sometimes the height requirement can still be a troubling thing for some plus size girls. So I would stick to focus on your images, you best assets, your energy, get great photos that show your diversity and be realistic with yourself. You might not rock the runway each season, you might never ever be on a billboard, but modeling no matter your height or weight, or size, or color is a tough world...so be prepared!
This agency in NYC does see plus size models.
Here is a list of some more world wide Plus Size Agencies.
Ford models also has a plus size but they do have a height requirement.
I would look into commercial print agencies that work with models of all heights. I would also look into Talent agencies, visit www.backstage.com and get a copy of the ROSS Reports.
Make a compcard and mail it out, keep hustling!