If you don't stop to knock on the door you can cover a lot more area. I suggest leaving flyers with an actual quote rather than just general company info. Those have been very effective for us.
Do your subs typically have common areas to be cut? If so, knock on a few doors and ask who to contact in the Home Owners Association. My experience is you knock on maybe 5 doors or so and some one will cough up the name of the HOA president (or other board member) just to make you go away. Those are they guys you want to talk to in person. A lot of times they'll just point to a house and say "it's that guy." Write down the address and look up the person in Whitepages.com.