Subaru doesn't really have a chain of dealerships and service centres. Instead it uses a few private garages already specialising in Scoobys, who will source parts directly from manufacturer. These places are approved by Subaru Japan, but they can cost a bomb, both parts and labour. Either way here is the Subaru dealer locator - http://subaru.co.uk/dealer-locator/
Flat 4 Online - http://www.flat4online.co.uk/ - Endless catalogue of Scooby replacement parts and upgrades.
Import Car Parts - http://importcarparts.co.uk/ - Great site for finding small and rarer replacement parts like bushes and clips. Can also be found on eBay [http://stores.ebay.co.uk/Import-Car-Parts-Japanese-Car-Parts], with parts often cheaper than the website!