The major US manufacturers of graphite are Mersen, Graphtech, Americarb, Carbone of America, Carbon Composites, Graphite Engineering (part of Mersen ), Morgan AM&T, MWI (Tokai), Poco a Div of Entegris: German are SGL and Schunk and Japanese are Toyo Tanso,Tokai, Osaka Gas, Kureha, Nippon Carbon.
Some of these have more technical expertise and spen on R a& than others but you could stast with these.
The largest are SGL, Mersen, Graphtech, Toyo and Nippon I believe.