Stefan,
Kit part supplies are limited. Body parts almost non-existent. Various trim and roof/side curtains for FiberFab cars are available from MG Magic. https://mgmagicclassicmotorparts.com/
Some trim pieces are reproduction TD parts. Headlight shells, door handles, stuff like that. Moss Motors is a good place to turn. https://mossmotors.com/
For the VW mechanical stuff, there are plenty of sources. A quick search will turn up multiple sources for almost anything you could need.
Always feel free to check in here before you buy anything, particularly if you are unsure if a particular part is correct for your car.
Paul Mossberg
Former Owner of a 1981 Classic Roadsters Ltd. Duchess (VW)
2005 Intermeccanica Roadster
If you own a TDr and are not in the Registry, please go to https://tdreplica.com/forums/topic/mg-td-replica-registry/ and register (you need to copy and paste the link)