If Lazarus shows up in John's probate papers isn't that enough to "tie" them to John Findley? If not, have you looked for Lazarus and Amanda's marriage record? That and the mention in the probate should be enough?
You might be able to find John's death notice in the Monroe County newspapers that are free at http://monroecounty.advantage-preservation.com/
The Monroe County Iowa Genealogical Resource page, www.iamonroe.org/
has inventories of some cemeteries.
The Monroe County Iowa Genealogical Society, www.facebook.com/Monroe-County-Iowa-Genealogical-Society
has records too. Successful Searching & happy holidays!