The only one I can find is built-in into TS12
TS12 (release reference : version 3.7, service pack SP1, build 58414) according to the Trainz Kuid Index.
My recommendation is to download any K5LA horn, edit the config.txt file and replace the kuid with the downloaded one. You need to replace the line twice so use a search and replace function in your editor.
Once edited, save the config.txt file and submit the asset.
