This is a way of re-batching soap using any soap you choose. It can be new or old store bought soap, hotel soap, left-over bits of soap that are too small to use anymore, or your own homemade soap. You shred it up in a food grinder or use a cheese grater to grate it. You can also buy grated soap in packages in some stores (I rarely see it though), or online if you don't want to shred your own. Sometimes it's called 'soap noodles'.
I have used cocoa powder (for making cocoa to drink) as a brown colorant in soap in the past and it works well.
For a fragrance oil, since this is a recipe for a re-batch of already saponified soap, you can use any skin safe fragrance oil. They can easily be found online. A couple of craft stores I have been to do carry some fragrance oils to be used with melt & Pour so if you could find a chocolate FO in one of them, that would work. But I have not seen any chocolate FO's in those stores, which doesn't mean they don't have them, but their supply is so limited, I'd say you would have better luck online.
Speaking from experience, I have made re-batch soap with grated store bought soap. It was a fun project for my grandchildren one summer. We bought & grated some Dove Bars (if I remember correctly that was the only soap sold in the little store near the cabin we were staying in at the lake). They chose their own additives from the pantry and individualized their soap to their own liking. We used yogurt containers as soap molds, greasing the insides lightly to make un-molding easier.