Order the set, flog the spare?

Unless you dont mind getting one from our usual suspects in China, then I would say the CNC4YOU price is probably the best you'll find from the UK, your buying support with them to!

You can find a few Chinese suppliers selling on eBay, they use various European warehouse's so delivery times to the UK can be quite good, as well as the price.

Be careful though, there are quite a few Huanyang copies knocking about.