Here's some links to other sites which you may find useful:

http://silverbackrcproducts.com

Silverback RC Products Ltd have been designing and manufacturing aftermarket parts using the some of the toughest engineering grade polymers possible for the popular HPI Baja 5B, 5T, and 5SC models.

http://www.innovative-rc.co.uk

Innovative-RC are a manufacturer of many aftermarket parts for the HPI Baja. From Aftermarket chassis to Big-Bore shocks you will find it here. They also stock a wide range of engine spares and parts.

Bashing Groups & Clubs:

Irish Bashers
As the name suggests a group of guys in Ireland doing what Bajas do best.

http://www.northeastbashers.co.uk
Holding events all over the North-East of england.

http://www.northwestoffroadrcclub.co.uk

 A club with many daily events covering the North West.

Farnborough Bashers
Dedicated bunch of guys, check the link for meetup locations.

South-Coast Bashers
Organized bash days in the South-Coast area.

North Yorkshire Bashers

Daily events and track setup in North Yorkshire.

Bawsey Bashers

Group of guys in the East of England.