When starting the building of a playground, or anything, it is VERY important to go to the media. You want the people to know what is going on, therefore, keep them informed and you will be out in front. Every time a person sees something or hears something through the media, it is taken seriously. The more it's put out there in the media, the more the person will remember it, and become more interested in wanting to know more about it.
Get someone who has a background in journalism, or public speaking, send them out armed with all the information, to talk to the media. Get the word out there that you exist and make sure the public knows about it, because with only you and you alone, it will be very hard to get the trust and help you need to achieve your dream.
Put the word out to all forms of media, television, radio, newspapers, even the clubs which have newsletters, spread the word in every way you can, it's well worth the effort. Also, try the unions, they all have newsletters sent out to their members and from there you may be able to get the help you need in different areas. Anything is worth a try.