I doubt there is any Research or Commercial operation Now buying...

I doubt there is any Research or Commercial operation Now buying a single Tonne of graphENE.
as said b4 Haldane of the UK may be selling product using graphene and of course there's  the existing tennis racket market. maybe googling tennis rackets will  give a Tonnage and price NOW figure
but of course SL Vein is quality beyond the Tennis Racket Market, surely?

Anyhow the BIG Market for graphene is in strengthening/improving Building Materials like cement and steel.
Unfortunately it takes years and years to get gov't approvals/tests done to manufacture and sell new building products.

anyhow offline now so @heraclitus and @nihilism there's some chat on research 'leads' for you on current graphene sales of production.
Weekend will give my opinion of Warwick Grigoretc. "Lost" his last name for a mo. got stuck on Warwick Capper, a double innuendo, hey?