Hello and welcome.
This is a question that somes up very often, and so far nobody has ever returned to say they found a park to accept it.
Your best bet is to google "sites that accept bring-ons" and then telephone the sites directly/
Be aware that even sites that say the accept bring-ons usually only take them if they are coming from another site, not if purchased independently, and only take them when they have empty pitches that need filling - so will probably only give an annual lease, meaning that next year you may be looking for yeat another site.
It could be cheaper/easier/quicker to sell/scrap the existing van and buy another direct from a site you like.
Unfortunately you are one of many asking this, and the short answer is that you will be hard pushed to find anywhere in Britain. Condition means nothing to site operators, only age matters, and most seem to have a maximum limit of 10 years, and that's only for those they have sold. 20 years old is way "past it's sell-by-date" as far as most sites are concerned.
Apparently the same doesn't apply in Europe, they are far more flexible over there.
As has been said, this is a frequent question: try searching this very forum to see the many comments over the years.
Good luck, but the pitches you’re looking for are like hen’s teeth.
Yes try the Search Facility and play about with the wording of your search.
And tick'all words' as opposed to topic subject when looking.
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------------- XVI yes?
As well is two words!
How does a sage know everything about everything? or does he? or does he just think he does?
Remember, if you buy something you bought it, not brought it.