The name may very well be Scottish.
Black, 'The Surnames of Scotland, Their Origin, Meaning and History' has these entries:
BLAYLOC. A rare name recorded in Annan, 1801. Suggested to be from OE.
blae meaning livid or lead-colored hair, but perhaps of local origin. Cf. under Blellock.
BLELLOCK, Bleloch, Blelloch. Of local origin from some small place of the name. There are two places named Blelock in Perthshire (in 1652 Bleloch), and Blelack (in 1657 Bleloch) is a farm name in the parish of Logie-Coldstone, Aberdeenshire. There is also a Blailoch in Selkirk Retours (1687)
And there is also this:
http://www.surnamedb.com/surname.aspx?name=Blaylock