This method does have some success if you are willing to pay top dollar and you want to work at it.
I do this on occasion to locate sites for childcare centres. However, I have a buyers agent approach the owner. Their approach is to send a letter first, if there is no reply they send a second. If there has not been any contact they then give the owner a call. If that fails they do a door knock. Dropping a letter and then calling is a better approach that way the owners don't think you are a cold caller and have some familiarity with you when you call them.
I have fed through 10 properties over 4 months to the buyers agent and unfortunately we haven't had any success. There has been a mixed response from people where some want $2,000,000 for their property when it is clearly worth $1,500,000 or I have offered 100% more than the properties worth and the owner won't budge. In this particular situation these properties are unique so they do deserve a premium but I am in no rush and eventually it will work.
Note: The buyers agent gets 1% of purchase price if there is a successful exchange.
It really is a 1 in 100 exercise so it will take time unless you get lucky.