I’ve been to Amish church services. I would suggest looking at some of the smaller communities and not Lancaster County, PA. There are some nice smaller communities in Ohio and in southern Ontario. If you do a bit of searching in the internet, you can find a family that runs a B&B. Perhaps then you can begin a dialect of communication over the internet with a family and discuss options for your visit and how much they would be willing to let you contribute without getting underfoot. Winter is a good time, because in the Spring, Summer and Fall they are involved with their gardens and farms and usually don’t appreciate outside help (usually because outside help mucks things up and then they have to waste time fixing it) If you have any farm experience, that might help aid your request. I have a lot of farming experience, so perhaps that is what made a difference for me. If you smell like a tourist, they most likely will not be interested. Like me, I just don’t have time for tourist when I am busy trying to work my farm.