I got mine here, when I had my 1.8 probably the best price. Fitting is a doddle a local garage should charge around £40-50 if you don't want to DIY.Firstly, not sure if this is the right place for this.
I'm trying to find a shop in the Dorset area - near Poole/Bournemouth if possible that sells the kits. Google didn't bring up much.. I'm after getting one tomorrow you see...
Thanks anyway x
K&N 57i Induction Kit Honda Civic 1.8 2005-2011 57-0668 | eBay
I tried getting mine local but no where seems to stock these kits, many places will be happy to order them in but usally works out more than eBay.