Sorry that I didn't get back to check on this query.
Colvin Cemetery is on Hwy 79 North of Ashburn, MO..
It is part of the old Busch(Droste) Farms.
Probably easier acess off of Rte. T.(going to New London, Mo. Cemetery supposedly sets in Sec. 3, 56N, Rge. 3W
Don't know if anything remains as I just have a map showing it. I've never been there