sanding paper, 1200 and 2000 grid, cheap and easy.
I would start off by trying a small pocket knife and looking at some youtube vids about convex sharpening.
Good trick to test the sharpness is build a small square out of wood and pull some elastic bands over so the middle is covered with the elastics mimicing the veins and arteries. Push your Bhead through and watch if the rubber bands get cut.
When they are pushed aside, your Bhead needs sharpening.
F