The heads themselves are called micrometer heads, and occasionally you see complete tables on ebay - These are often listed as "microscope stages" or "miniature table". One such example is here
Originally Posted by verney
A slightly more crude table can often be found in machine tool dealers listed as a "two way vice" or a "cross vice" - See this offering for a picture. These do not offer the precision of a microscope stage, and many of the chinese made offerings are, for the want of a better word, crap quality.