There is no such thing that exists. Newer cars actually you cant barely hear them with good ears. Reliant on remembering/seeing the flashing light on the dash.
Only reason why flashers were audible wasnt just so they could be heard (just a side effect). It was because of both the flasher design just being loud during operation and the lack of sound dampening of dash design. With the aim for quieter cabins and changes in flasher designs they are inherently quieter.
Hondas have always been a quieter flasher design as well.
Now you could probably find something you could wire to make a beeping when turn signal is engaged but there is nothing I have ever heard of specifically to make the flasher itself louder