Bloody Stupid GW UK Online Stores...

All I want is a single Eldar falcon engine block sprue for my Vyper/MkII Colonial Viper conversion from the GW UK online store. Should be easy enough but no, they don't sell the three different falcon sprues seperately. The US store does, but absolutely nowhere else. Even I'm not enough of a convertaholic to shell out £20 for two tiny engine parts. I'm going to have to go back to the drawing board with this one.
Why is it every time I desperately need a part it goes out of production about a fortnight earlier?