Previously, we have recommended RJ12 connectors for LocoNet cables.
While there have been online sources such as Digi-Key, Mouser and others, they have become harder to find locally.
There now appears to be a easily available alternative.
Many national big-box home improvement stores have RJ11 6P6C meaning they are 6 position 6 conductor and can be used as RJ12 although labeled as RJ11.
These must not be confused with four conductor connectors since LocoNet has six conductors.
You will need the connectors, the six-wire flat cable and a crimping tool.
We paid $20.00 in February, 2008, for such a tool at a store.
Presumably, other such stores will also have these items.
There were more expensive crimping tools, but the one we bought was mostly metal and looks to be durable.