If your going to look for an auto- factor to see if they can supply you with paint I would also consider seeing what your local agricultural/marine suppliers have in stock. The agricultural paints will have far more "guts" (body)than anything your auto -paint supplier can supply and there is now a surprising array of colours to choose from.
When I moved house about 20 yrs ago I had loads of tins of the blue and grey Hammerite in my workshop, I think there were even some green ones and tins of white Tekaloid that were all from the 60/70s and in very rusty tins. I had a massive bonfire and put the lot on it
. I regretted doing that years later especially getting rid of the Tekaloid.
poppydog