Hi, does anyone know of anyone who can supply and fit a pop up to my '94 super custom living saloon. I have a growing family and the whole point of having the van was to avoid tents.

I'd guess one of the custom camper van converters should be able to source and fit one. Try a camper outlet and see if they can advise.

Don't know your location but these guys in the UK might be able to help.
http://www.wellhouseleisure.com/
I have no personal knowledge of them but seen a feature about them on one of those Sky channel programmes (Caravan show or whateveritscalled) and they looked quite professional. They import Japanese vans and convert them.