Just got the latest "Sporting Goods Dealer" magazine listing manufacturers. Here's who it lists under baseball gloves: Adams, Akadema, Bomark, Brett Bros. Controlling the Game, Diamond Sports, DeMarini, Easton, Franklin, Glovesmith, Hillerich & Bradsby, Markwort, Miken, Mizuno, Nocona, Pinckard, Rawlings, SSK Sports, Venus Knitting Mills, Wilson, Worth.
One doesn't see the older big names like Spalding or MacGregor any more. The above list probably reflects mainly the U.S. based companies or those who have a presence here.