If I am understanding your question correctly, you are looking to establish your cleaning business? I recommend that you contact businesses directly. Be prepared with your rates on a professional flyer-including specific cleaning services that you provide. Good luck to you.
I'm not familar with purchasing contracts but I am aware of a process where you can bid on projects through an annual contract. You would be best served to contact the William Factory Small Business Incubator they can stear you in the right direction. Good luck with your Venture$$$... http://www.williamfactory.com