Welcome to LZ.
Richards and Marsland are the established makers of galvanised chassis, there is also an Irish company called Shielder, but opinions on them are mixed.
Can't help much with the fitting, I don't know the area. But there are a lot of garages that will do the work. You will need to assess the bulkhead too, if it is very ropey there isn't much point in putting it back on, better to get that reconditioned before the rebuild as well.
This section is for Introductions. If you want more suggestions about local mechanics, it might be better to post in the South East section, or in Series Landrovers.