I have been using some DMT 3"x8" diamond hones.They are basically a 3/8" thick steel bar,impregnated with diamond on one side and,are fairly expensive.
If you want to save some money,get some "wet or dry" sandpaper,one sheet each of 220,320,400,600 or as fine as you want to go.Lay the sandpaper on a hard,flat surface like glass,ceramic tile,steel plate,formica etc.You would be surprised how long that sandpaper lasts.
I did a "How To" in the "How To" section on sharpening Grizzlies using the paper.