Is there a place where I can get free source files for my audio JSX tag?
have you tried googling it with some phrases such as “free sounds to use” or other related to see what shows up? there are quite a few where you can download sound bytes from those sites for free.
or you can try looking into other implementation and take a look where they have taken those sounds from and use them in yours.
happy coding 
Freesound (community-uploaded audio under Creative Commons)
Free Music Archive (music + sounds, many free to use with attribution)
If you just need test files, you can also generate a small .mp3 or .wav yourself and place it in your public folder, then load it with your tag.
That way you’ll always have something working for your JSX audio element
Hope this helps🙏