It's funny you know, despite never owning a grey/white FC (plenty of other colours over the years), I have original cans of paint for both these colours in my garage. Absolutely no use to man or beast of course (although the contents are still liquid, even after 50 years!)
Have a look at this thread
http://fefcholden.org.au/forum/index.php/topic,5310.0.html for details of how you can obtain the two-pack or acrylic formulae for these colours.
cheers
RET
(It's interesting - both Volcanic Grey and Granite Grey appear to be the same colour according to the label, and it also passes as what I assume must be Ford Gibraltar Grey.)