What if your mini happens to be Ferrari Rosso Red? where is the best place to get paint made up?
You should be able to go to a paint suppliers, i.e. one that suplies bodyshops.
If you dont have the paint code they should be able to match it up using swatches they have.
If you have the paint code Halfords can also mix up cellulose at abotu £10 a litle, or in spray cans.