To have work done to my car I use SlowBoyRacing near brands hatch which is pretty close to you too
With regards to parts etc if i see something on someone's car i like whether it be in the flesh, on a blog, magazine or forum like here i normally just Google around for the best price and get it that way!
I do have a massive list of sites on my favourites folder to get bits from mostly uk sites but a couple of yank and japanese ones...... stuff I've ordered from Japan normally gets here quicker than stuff from the Uk which I still don't understand how!!!
Here's a few sites to keep you going!!
www.nengun.com
http://www.scoobyworld.co.uk/
http://whifbitzperformancetuning.co.uk/index.php
http://www.scoobyclinic.com/
http://www.scoobyparts.com/
http://www.grahamgoode.com/
http://www.sumopower.com/
http://www.lateralperformance.co.uk/
http://www.amber-performance.co.uk/
http://www.rogerclarkmotorsport.co.uk/
http://www.rhdjapan.com/subaru/gda-g...exterior-parts
http://www.flat4online.co.uk/catalog/
http://www.japanparts.com/
http://www.tdi-plc.com/catalog/subaru-c-107_1296.html
http://www.burtonpower.com/