Fred Gosbee and I (Castlebay) often write about local Maine history and legend. We also work in schools to help kids wriet songs about their local history. They dig up the stories, sometimes interviewing the elders, we coach them in the songwriting then it's all presented in a public concert. Christopher Shaw used to do this in the Adirondacks where there's a story under every doorstep. It's a great way for kids to relate to the elders, process info, and understand their local history and the fact that we are all part of history.

As far as getting people to lend you their diaries etc, they need to feel secure and trusting about it. We recently had a public event that honored the local elders and their stories. Once they realized that people were actually interested they were very forthcoming.
Establishing an ongoing relationship with the local retirement facility by volunteering might be fruitful.
Good luck

Julia