The problem with the UK is that people don't seem to want to repair things unless they can get the part and do a direct swap. With something like an exhaust I would've thought that anything will do so long as it's long enough to stick out the back and fits without touching anything. People with their raced up cars stick all sorts of exhausts together and you could join them and go with a straight through cherry bomb but it will be noisy
If you went into kwik fit or somewhere like that, stuck your van up in the air and went through their stock you could come up with something that worked but will they want to do it ? That's the question, the computer will probably say no.
There are generic exhaust boxes and pipes that you can buy at places like this https://jetex.co.uk/ and sticking universal exhaust rear box into ebay will get results or maybe try Toyota, but I gave up hope with them a while back and they also annoyed me by refusing cash. With the parts in hand you've got a good chance of a better result when turning up somewhere and asking to have them fitted.
I am rapidly heading into the realm of if it doesn't have to be exactly the same then what else will do instead... Good luck !
ps. I've got the same van as you and would be very interested to know what you got to fit, just in case mine decides to give up on life too.