substitute for unsweetened cocoa powder (chocolate cake)!!!! urgent!!!!!!!?!

hi i am in yr 8 and i have o make a dessert: double layered chocolate cake , i dont have unsweetened cocoa powder and i dont have buttermilk either, he dont do it in Asda!!!! please could you give me substitutes urgently as im cooking on monday!!!!!!!!!!! please helppppppppppp someone ... Thank you!!!!!!!!!
the recipe is below:

Step 1: You will need:
? for the cake:
? 85 g dark chocolate , chopped
? 360 ml brewed coffee , hot
? 350 g flour
? 600 g sugar
? 120 g unsweetened cocoa powder
? 1 tsp baking powder
? 2 tsp baking soda
? 1 tsp salt
? 3 eggs
? 180 ml vegetable oil
? 360 ml buttermilk
? 1 tsp vanilla essence
? for the icing:
? 170 g dark chocolate , chopped
? 170 g milk chocolate , chopped
? 450 g crème fraiche
? 2 tsp vanilla essence
? a pinch of salt
? 1 saucepan
? 1 whisk
? 2 bowls
? 1 mixer with a whisk attachment
? 1 spatula
? 2 x 25cm round spring form cake pans
? 1 wooden skewer ? Serves:
? 8
? Preparation Time:
? 15 minutes
? Cooking Time:
? 1 hour 30 minutes
? Oven Temperature:
? 150° c - 300° f
1. Step 2: Preheat the oven
Set the oven to 150oC (300oF/ gas mark 2) in preparation for baking.
2. Step 3: Melt the chocolate
Tip the chocolate into a bowl. Pour over the hot coffee and whisk continuously, until the chocolate has thoroughly melted.
3. Step 4: Combine the dry ingredients
Add the sugar into a separate bowl. Follow with the flour, cocoa, baking soda, baking powder and the salt. Mix it all together into a finely combined powder, by twisting it with your whisk and set it aside.
4. Step 5: Combine the wet ingredients
Put the eggs into the mixer. Whisk them on high speed until fluffy. Slowly pour in the oil, little by little. Make sure that it has fully incorporated before adding in the next batch. Add the buttermilk, vanilla and the melted chocolate and coffee liquid. Add it in slowly as it will splash back!
5. Step 6: Add the dry ingredients
Slow down the mixer and carefully spoon in the dry mixture. Allow it to mix until it's just combined and remove the bowl from the mixer.
6. Step 7: Bake
Pour the batter equally into the two cake tins and transfer them into the oven. Bake for roughly 60 minutes or until done, then remove.
7. Step 8: Test the cake
Insert the wooden skewer into the middle of both chocolate cakes, to see if they have baked enough. If it comes out free of batter, they are done.
8. Let both cakes cool down completely. In the meantime you can make the frosting.
9. Step 9: Make the frosting
Heat a saucepan, one third full of water and put a bowl over it. Spoon in the dark chocolate and the milk chocolate.
Stir it until they have melted. Add the crème fraiche, the vanilla and the pinch of salt. Mix together with your spatula until thoroughly combined and remove the bowl from the pan.
10. Step 10: Frost the chocolate cake
Allow the chocolate spread to cool and begin to solidify before frosting. Occasionally whisk it to maintain the same consistency. When cool, take one of the cakes and using the spatula, pour over some of the frosting. Spread it generously but evenly all over the sponge. Place the second cake, upside down over the top of the first cake, removing the baking paper, as you go. Finally, spread the remaining frosting, liberally and evenly over the top and sides of the chocolate cake.
11. Step 11: Serve
Your chocolate cake is now ready to serve. Slice and enjoy it as you would any other chocolate cake, as a sumptuous dessert or else as an indulgent mid-morning snack!