You want part number 3143 from Port Lines, it is $85 but is the complete electronic system.
I haven't been able to local the repro -- if he still has them. However I did get to where Tom is mentioning. Being a cheapo, I like the $45.00 style. My recording ended with "and all points west", would that be the westbound version? Though it might be fun to have all 4. How does that work; rotates through them one at a time?
I'm guessing this is a little unit one could put anywhere, like even in an old Plasticville suburban station...