As far as I remember (and I am getting old) you can call any business and ask if they want a window cleaner.
In the old days, you could buy any type of commercial mailing list, from a reputable marketing company, (not sure now) and send them your leaflet.
You can also email any company and ask them if they want a window cleaner, but you have to give them the option to 'opt out' of any further emails from you.
I seem to remember Becky Swan was cold calling commercial work, not sure now.
Personally, I would design a leaflet, specifically for commercial work and find a very good distribution company that will only target commercial work. This is where you will score!
Just to add, I would probably use Royal Mail to deliver; I reckon these are the only people with a good enough database (and ability to deliver to commercials). It may cost more to deliver, but you know it's 'job done'!