Hi Leah
I doubt you’ll be able to buy it off the shelf in Tiverton….or anywhere in the UK because the powder/raw material is classified as toxic (don’t worry – the solution we/kids use is so diluted it is harmless!). You can buy it from a well known auction website – search for Sodium Tertraborate, or a chemical supplies company. Some people use contact lens solution – but check it contains boric acid (similar to sodium tetraborate) as an ingredient – you’ll be able to find that in Tiverton although this isn’t really as good as borax.
Ruth