Bearing balls use a numerical grading system that indicated roundness and tolerances. The lower the grade number, the better the roundness, etc. For example Grade 25 balls are "better" than Grade 100. For bicycle use, Grade 200 or better is perfectly satisfactory but, as FBinNY noted, the cost difference is so small so most mechanics will use Grade 25 balls.
All the big bearing manufactures (SKF, Timken, etc.) make bearing balls but finding a specific brand name is difficult since they are only sold directly in very large quantities. So the ones you find in reasonable numbers (packages of 25 or 100) in bike shops or on-line dealers are repackaged by distributors under either a generic on distributor brand name.