Can't see why ordinary mains twin and earth flex wouldn't work, though it looks pretty unprofessional. One good idea is to fit a length of 7 strand trailer cable.
the cables on my rev counter were no thicker than telephone cable trailer wire may be a bit bulky as it is designed to carry more load than the gauges would ever need. something inbetween trailer cable and phone cable. 3A cable should be plenty for gauges
This is how I fitted them to my old bus Chug Chug:- http://www.volkszone.com/VZi/showthread.php?t=397525&highlight=chug
as said automotive cable is designed to be more flexible than household, on my old van i ran a 13 core euro trailer cable front to back for additional toys.
