Try Halfords or similar car spares for a suitably sized drive belt,
Failing that most towns have a bearing and drive belt suppliers who should be able to match one up for you.
The drive belt on the Elf is a multi ribbed belt and you will need to source one from a specialist supplier now - If your elf is missing the belt altogether let me know and I will get you the sizes off the one on the Elf I have in storage in my workshop.