You cannot get their WAVs for free, but you can replicate their sound for free. Here is a DIY guide using open-source tools and royalty-free platforms.
If you are familiar with BOOM Library, you know they are the gold standard for sound design. These aren't amateur recordings; they are pristine, high-fidelity WAV files that sit perfectly in a mix. There is no hiss, no background noise, and no muddy frequencies. It sounds expensive, even though it costs nothing. boom library anime essentials wav free