Here are a few companies and sites that can help with Dormobiles or Carawagons. I'm sure there are more so please post any details that may help Dormobile/Carawagon owners.

Dormobile Parts
The Dormobile Company was purchased from the receivers in 1997 and is now owned by SHB Hire Group.
A lot of parts including the roof can be purchased new (shipping from the UK may be prohibitive !).
Dormobile Ltd - Lifting roof conversions for Land Rover, Bedford and VW, parts and spares

You can download a parts/price list from the site.

Seat Covers
Exmoor Trim make the correct Elephant hide seat covers for Series II/IIa Dormobiles.
Front Seats : Doormobile retrim kit

Curtain Rails
The correct Silent Gliss curtain rails etc. for the Dormobile can be sourced from a number of UK suppliers. Silent Gliss have a NSW office who passed me onto a VIC agent who wasn't really interested.

I used The Trim Shack who specialist in Volkwagen Dormobile curtains etc.
Silent gliss curtain tracking from j&s

Forums & other sites
There is a Land Rover Classic Campers forum in the UK.
This covers Dormobile, Searle (Carawagon) plus any other aftermarket camper conversion.
Land Rover Classic Campers

Terri Anne Wakeman has a lot of Dormobile & Carawagon information on her website.
TeriAnn's Expedition Land Rover site

Dormobile Owners Club
Dormobile Owners' Club Home

Military Carawagon
EMLRA Vehicles - The Military Carawagon