You can find 82 free hdri skies, and many more soon.
Please have a look, I hope you will find it useful. Just click on the image to get there. It works as a web store, so you will need to add some products (free hdris) to basket and create order. Everything else works the same as on my main webstore hdrmaps.com.
You can use it also for commercial projects, but you can't redistribute or resell any hdris taken from my sites.