http://www.annajarvishouse.com/index.html, which includes written history and images of the inside of the museum. A link from this site will take you to the International Mother's Day Shrine (http://www.mothersdayshrine.com/). This website includes a more detailed description of the history of the holiday.
It just goes to show you, there's probably a museum (and it's probably got a Web presence) for every subject under the sun. You just have to go looking. Whether or not they provide valuable resources is a judgement call you'll have to make.