Hi all

I need to do some marketing for my cleaning business. I have read some threads here which are related to my question, I can see that go out and knock on doors or cold calling are the most effective way.
So I have started knock on doors, then here are the problems that I currently have: my cleaning business is focusing on general commercial site cleaning, and office cleaning. When I did my door knocking in my area, I have found most of the companies have "no sales person/ no hawkers" sign on their front door, so I can't go in and sale myself to them. What is your suggestion to find clients in an area like this?
Oh, I forgot to mention, I was trying to approach these offices by mail, I have designed some sales letters and was going to drop into their mail box, but I found that the whole complex's mail box has "No Junk Mail" sign on them... damn they are well protected...

I am also planning to find some school cleaning or office building cleaning, can any one advise when I make calls/or walk in to the reception who should I look for? What position of staff is generally in charge of hiring the cleaning companies or is the decision maker of the tender?