Well, where would you get parts for any other car?
Most motor factors stock general spares for the Elgrand now. Most service items are available including brakes, bearings and bushes. The BEST place to get your parts from is BMR (
https://bmr-automotive.com/). He's a member here and will do his best to help. In some cases he may not be the cheapest, but that's because he doesn't sell cheap shit parts that will fail after a few months. He's an enthusiast and a mechanic, the best kind of person to buy from when taking care of your car.
As for other bits like body parts, bumpers, lights, seats etc. You are going to have to go to a breakers yard. There are plenty of places in the UK that are breaking Elgrands. I don't know them all, but there is a good one in York, or there is the Elgrand Warehouse in Cornwall. Expect to pay a lot for body parts. They are big and scarce. An E50 Rider bumper will set you back Ā£600. An E51 Rider bumper will set you back Ā£1000. There's an idea. The best advise here is... don't crash it or prang it! Often repair is cheaper than replacement... so look into quotes from body shops when possible rather than looking for replacements.
Aside from this, the alternative is to get the parts from Japan. This is possible, but expensive. There are a few places you can go to who regularly import parts. Ask them for a quote and they will get them over here as part of a bigger order they are placing. This will help with shipping costs etc. Delivery time from Japan can take a few months though, so don't expect it here next day.
As a closing statement... don't worry too much about it. We have 1400 members and all of them have been able to get what they need.