I am another who has a good selection of old auto paint related info. This is mostly just general catalogues and colour charts from the various paint manufacturers around in the fifties, sixties and seventies but I have a few Rootes specific items as well (and I think somewhere I may even have saved some interior fabric swatches).
I'm also in touch with several professional restorers and painters and they can often provide hints or other contacts for methods to match old to modern. My most recent paint purchase was via a specific 'RAL' code which is some sort of universal standard that should ensure that you get a pretty close match each time you order a quantity, regardless of who supplies a particular batch.
I also have a small stash of original Rootes/Chrysler colours in cellulose. These are mainly one pint tins and in most cases there would only be enough for touch-up levels of activity. Seacrest Blue anyone? However, this is very much a personal hoard with some amazing seventies metallics included and I'm not really fishing for opportunities to move any of it on just yetawhile.