Ask them.
Many Amish, when they decide to retire, move to Florida.
Some farms become too surrounded by development and the price per acre is
high enough to tempt them, especially if they want to move to a settlement
where they are opening a new church, like in Canada, or in the mid-west.
You may find the farms are beautifully cared for and the soil great for
food production. However, the land may also be saturated with
chemicals/poisons, if that matters to you. Do not expect the price per land
to be cheap.