Which controller is needed to operate the Bachman Rio Grande battery operated train and where can I purchase one?
If you are asking about a large scale Bachmann manufactured radio control 4-6-0 Big Hauler, the road number on the locomotive indicates the transmitter's frequency, 7 for 27 MHz and 9 for 49 MHz.
These are a few decades out of production. You can sometimes find them offered on EBay or at model train shows.