The first place you should always look for state-specific laws is the .gov page of the state. For example, in Maine you would look at www.maine.gov; likewise, in Massachusetts, you would look at www.mass.gov. Each of these sites has a map and a search function, which should let you find most of the state laws concerning both probate and last will laws.
For more specific information, you can search third-party sites, which may or may not have more information. The website Legalzoom has pages on state-specific laws, but they are for information only, and are subject to changes in state law. Here is information on Maine last wills. Massachusetts has a Law Library site; here is their page on last wills.
For probate law, a search for the state and "probate law" will give you most of the information you need. Here is a page for Maine Probate Law, and here is the Mass.gov Probate page.