There are codes that you can use in regular Google to limit your search to only certain domains, like town governments or nonprofit organizations. Here are some examples.
You'll need to adapt them, swapping in variations in keywords like parks or recreation for "open space," or other sites like "boston.gov" or "cambridgema.gov" to get at the towns that you are interested in.
1. Searching a town government:
open space site:waltham.ma.us
2. Limiting to State level government:
charles river open space site:mass.gov
3. Identifying Nonprofits:
charles river open site:.org
If you find the above types of searches helpful, you might be interested in exploring Google Advanced Search, which allows you to target your searches in many different ways. What happens if you limit "filetype:" to .pdf ?
Fun fact: if you ever forget how to get to Google Advanced Search, you can of course... Google it.