Hello
I don't know really where to go with this. I do have a few VHS videos myself but mostly from when Curbs was Charlton manager in the 2000s. The nearest one to your dates is 98/99 but Barnsley and Charlton were not in the same division then.
I would try some of the other fan sites like Charlton Life
https://forum.charltonlife.com/ where you might get some fans who know about videos from back then. This might be the best place to start as more CAFC fans use this one although there are others or perhaps they can point you in the right direction.
Failing that try CAFC directly
info@cafc.co.uk perhaps they would also know where to look,
Good luck with your research and all the best for the remainder of the season.