Schumacher still have the bodyshell available new on their website. Maybe still have some of the other parts you need?
http://www.racing-cars.com/scp/Old_C.../CAT_2000.html
Also Team Blue Groove do a repro version and the undertray to match.
http://www.ebay.co.uk/itm/SCHUMACHER...item2305dfafdf
Also not sure if this is the top deck you're after but.. :
http://www.ebay.co.uk/itm/VINTAGE-SC...item2c542b4ae3
And if you want bling CAT 2000 :
http://www.ebay.co.uk/itm/SCHUMACHER...item2c55271147