Hi All I’m new to this I have a discovery 5 but need to get some new trim for the rear doors the section I need is the part that surrounds the windows.
I have tried 1 place and they have said I would have to buy the whole interior panel £750!

Can anyone help?

Yes welcome...
ask in discovery section...

I hate to be the bearer of bad news but the D5 has not really been around long enough for aftermarket spares to become available. One of the main reasons that many of us chose to drive older LRs is that we can fix them ourselves and parts are easily and relatively cheaply available.
I suspect that there are only two sources for the part you need and they will be a Land Rover dealer (and £750 does not surprise me at all), or a scrapyard.
There will not be very many D5s being scrapped yet, but those that are will have been put there through RTAs and the parts coming off them will otherwise be in good shape. There are various sites on the internet where you can describe what you are looking for and the request is sent to most of the major scrap sites. If what you need is available they will be in touch. You might try these as a starter. https://www.1stchoice.co.uk/
Good luck.

Welcome to the forum