Finding slave records prior to the Emancipation Proclamation in 1863 is very difficult. Their births, marriages and deaths weren't recorded in county records. Also Virginia didn't start recording births and deaths until 1853 but slaves weren't included in those records.
You'll have to look through the land, court and probate records of William Scott to find any mention of his slaves.
You'll find Northampton County records on microfilm at the Library of Virginia, www.lva.virginia.gov/public/local/results
_all.asp?CountyID=VA197. Your local, public library can request the microfilm via inter-library transfer but it will be a lot of looking.
There is a movement to compile slave records and it's progressing differently in each county and state. I'd contact the following to see if they have any info.
Cape Charles Historical Society
PO Box 11
Cape Charles 23310 or 757-331-1008
Eastern Shore Barrier Islands Center
PO Box 206
Machipongo or 727-678-5550
Lower Delmarva Genealogical Society, www.ldgs.org/index.html
Historical Society of Eastern Shore of Virginia, www.shorehistory.org/
Eastern Shore Public Library, https://espl.org/genealogy-reseaerch/
Virginia Historical Society, Unknown No Longer; project to identify Virginians of African Descent database