You could look possibly at the standard bar for a van of that vintage (should be reasonably widely available), but often campervans have things like water tanks in the way of mounting these.
There are a few specialist fabricators around that can circumvent this. You don't say whether your 'van is a proprietary make, but someone such as Watling Towbars could possibly help.
Their off-the-shelf offerings go back beyond 1996 for certain models, see pricelist here:
Depending on whether it’s a SWB,LWB or Alko type chassis you could get one secondhand off eBay or local FB marketplace- if it’s the SWB you may find the one from the van/pickup may fit depending upon the van body overhang.