Hi Michelle
There is this possible census entry for him in the 1851 census:
William Armstrong 42, Dyer Employing 3 Men, b. Dumfries
Elizabeth Armstrong 45 b. England
Robert Armstrong 9 b. Dumfries
Maryann Armstrong 7 b. Dumfries
Agness Armstrong 4 b. Dumfries
Agness Barry 22, niece b. Kirkmahoe, Dumfries
Mary Thomson 56, visitor b. England
Mary Rae 18, servant b. England
Address: White Sands, Dumfries
Monica