From
SeigelQuote:
In a speech before the Royal Philatelic Society of London, John R. Boker, Jr. estimated that 6,000 New York provisional stamps survived, of which 300 were uncancelled. Philip T. Wall later modified the count to 5,500 surviving copies, of which 500 were uncancelled.
Of the 5000 used copies, I would guess there are no more than 2000 still on cover.