Yes, there are some and, the terms and conditions vary.
In some cases, they are totally free, meaning use as you see fit, the author does not require money nor attribution credit.
Often, the author requires attribution credit (he/she is an author/contributor) but, nothing other than that.
As far as finding them, there are some sites on the web. I just use google to find them. You'll have to sift through some "junk" but, it's not bad (at least it wasn't the last time I did - a few years ago.)
HTH.