Have you tried sites like https://www.freesound.org
? c: The sounds are easy to download.
Maybe you could find something on youtube as well and download that.
Or use a sound that's kinda similar and edit it ? (I'm not sure which software is free though)
If you have something to record it with (and if your environment isn't too noisy), you can try to make a similar sound yourself using different objects. A bag with flour (and squishing it) is often used for footsteps, maybe with some editing you can make it quite accurate?