Any good quality low-capacitance coax will do fine IMO, your installation will define how thin or flexible you need it to be (i.e. are you dealing with a subchassis). The earth lead can be any thin equipment wire. Just be careful about that capacitance figure for the coax if you plan, as I assume you will with a 3009, to use an MM cart. Aim at about 75pF a metre or less.