Replacement part for 20-year-old Compass van

Try a caravan breaker. Here’s one and others can be found via an internet search.

http://www.alsonline.org.uk

Possibly more expensive if they do one to fit yours https://caravanpanels.com/

https://www.caravanbreakers.net/

& another one!

Assuming it's Plastic or Fiberglass,  have  you thought about finding a specialist repair company.  Plenty of them about that do it for car panels and bumpers. 

It's surprising what the Smart Repair specialist can fix at a fraction of the cost of replacement.