This is from the BBC good food recipes, and you can make buttermilk by adding lemon juice to milk, (not sure of the quantities) , but you could Google it.
Ingredients
170g/6oz self-raising wholemeal flour
170g/6oz plain flour
½ tsp salt
½ tsp bicarbonate of soda
290ml/½ pint buttermilk
Method
Preheat the oven to 400F/200C/Gas 6.
Tip the flours, salt and bicarbonate of soda into a large mixing bowl and stir.
Make a well in the centre and pour in the buttermilk, mixing quickly with a large fork to form a soft dough. (Depending upon the absorbency of the flour, you may need to add a little milk if the dough seems too stiff but it should not be too wet or sticky.)
Turn onto a lightly floured surface and knead briefly.
Form into a round and flatten the dough slightly before placing on a lightly floured baking sheet.
Cut a cross on the top and bake for about 30 minutes or until the loaf sounds hollow when tapped. Cool on a wire rack.