Have you looked at www.findagrave.com
for pics of their headstones?
If they aren't there, you can contact the Johnson County Historical Society, www.jchsiowa.org/collections-research/
and/or the Iowa City Genealogical Society, www.iagenweb.org/johnson/ICGSmemberData.htm
and one or the other will probably take pics for a donation to their organization. However I'd wait until spring before making the request. Successful Searching & Happy Holidays!