These have been made in the past. Not that easy to find now but they do still exist. If my old notes are correct here are the options:
1.) ERR Sound Converter -- Interfaces to and operates Railsounds 1 and non-TMCC Railsounds 2 (as well as many other traditional whistle/horn/bell systems. I bought two of them from ERR when it was shutting down, just before the transfer to Sunset/3rd Rail. Out of production since the transfer.
2.) TAS 1308 Whistle Controller -- Similar to above. Long out of production but can be found if you look hard enough.
2.) Digital Dynamics Equalizer -- Interfaces to and operates PS1 Sounds via TMCC, similar to above. Also out of production but can be found with a little searching.
Do you need more than what these offer?