Klaxon automotive horns, once standard safety equipment, disappeared from the roads after World War I.

If you want one, you can still have one.

https://www.amazon.com/s?k=klaxon+horn

If you really want a loud horn, you can get a compressor-driven air horn of the sort that trains have:

https://www.amazon.com/s?k=air+horn+compressor+auto