You can get the DMT diamond steel from
www.leevalley.com
for $34.50. They also have DMT's honing guide for $10.50: it's a little clamp-on guide that sets and holds the angle of your knife on the waterstone. They also offer a complete range of sharpening equipment and supplies.
You should sign up to receive their Tools catalogs: they have lots of kitchen equipment and utensils that are as imaginative and innovative as their woodworking tools. Twelve or fourteen years ago, when the very first Microplane wood rasp came out, they pointed out how useful it was in the kitchen. I bought one to try, and liked it so much I bought them for all three of my kids, since all are enthusiastic cooks. The youngest, a woodworker, uses his alternately to shape furniture and to zest lemons.
Mike