Whenever I'm soliciting cleaning clients, I usually use a call-mail approach.
First, I start with a list of potential commercial cleaning prospects. This can be either compiled or bought. Next, you write a very short point-form lead generation letter using the AIDA method. The points will mainly deal with problems associated with their current cleaners.
Then, I'll call in a week later to follow up by simply saying who I am, what I do, and how I can improve the process of keeping their office clean. This should start a discussion to get you the meeting with the cleaning prospect.