Rob,
Only the briefest of listings in my reference books:
Whisker's Arms Makers of PA: John Graves (with an "s"), 1769-73, Lancaster, gunsmith, (with further reference to S. E. Dyke's The Pennsylvania Rifle)
Gluckman & Stterlee's American Gunmakers: John Grave, Lancaster Borough, Lancaster, PA, 1773
Gardner's Small Arms Makers: John Grave, Lancaster Borough, Lancaster, PA, 1769-73
Similar information in Sellers but I believe you have that. Appears that this limited information on John Grave has just been republished.....
Bill