Any manufacture's stem would work. Look for the length you need and the angle. For angle, there are several "sizes". A zero degree stem is just that. It goes out perpendicular from the fork steerer tube, and there is not much that can be done with it. The other popular "size" is the plus and minus 6 degree (or sometimes 7 degrees). These are the stems that can be flipped. When "down", the angle of the stem approximates being parallel to the top tube. When flipped, it shoots way up higher. Look for one of these. Sometimes they will be advertised as 84 degree stems, (84 degrees plus the 6 degree offset gives you the ninety degree perpendicular to the fork steering tube). There is one more size, but I can't remember the angle. Also, there are adjustable angle stems available, but they are much more heavy than a normal stem.

I like Ritchy, but will probably go with Deda for my Pinarello build that has a Deda handlebar.