look at family search ny probate records, there are about 21 wills listed for Dunckle/Dunkil's in Montgomery County. Also look at the three rivers site: threerivershms.com This is a site with focus on Colonial timeframe in the area bisected by the Hudson river, Mohawk river, and Schoharie Creek.
You can also contact the Montgomery County Dept. of History and Archives in Fonda, NY. They have wonderful research facilities.