Extra large muffin cases can be a real pain to find. However, there are some online UK stores which sell them. www.cakecraftshop.co.uk is one of the best ones which do sell them. You can buy a pack of 50 jumbo muffin cases for �2.20 which is quite a good price. They don't seem to sell them in smaller packs though! They also sell the baking trays which the muffin cases go into. If you live in Kent, they do actually have two stores there so you could easily just pop in and see the range for yourself. If not, the website has everything you could possible need baking wise.
If you would prefer to shop offline, you should basically look around your local supermarkets, and convenience stores. However, your best bet is to shop online as you can usually find a lot more of a range than you usually would offline.
If you would prefer to shop offline, you should basically look around your local supermarkets, and convenience stores. However, your best bet is to shop online as you can usually find a lot more of a range than you usually would offline.