The key question to ask yourself about your park when looking for primary sources is, who cares? Who might possibly have a stake in your site and would have writing, photos, or other media about it?
This might include:
Note that this list isn't exhaustive, and it's not a guarantee that your park will be represented in any of these types of sources, if at all. However, it's worth the effort to see what is out there that you can use for your project!
The rest of this page lists some promising newspapers to test out. You should also visit the Finding Multimedia page to help you locate copyright-free images that you can use freely in your projects.