they are based around the caster racing buggys apart from the lay down shock towers so most parts are interchangable between them and theres quite a good support for caster in the UK,
http://www.junction8models.com/ and
www.apedmodels.com stock there stuff but you can buy the Rave spares straight from the importers web site:
http://www.centuryuk.com/Products/Ishima+Spare+Parts