found this paint from fastenal

1gal Old Caterpillar Yellow Stops Rust® Industrial Enamel Paint
www.fastenal.com/products/details/0136239

protec coatings make a full range of industrial enamel in colours for the major brands and have all the classic tractor colours everything form old and new cat yellow to jd green and ih red. your stockist can also mix you whatever colour you like if you have a sample from 250mls to 20 lts. they also can order bulk drums of the ex factory colours for you.

any good paint shop will mix you a colour based on a sample piece just give it a clean and shine it up with a little car polish so its not dull and they can match to that.

bareco also supply equipment enamel in all the common colours including stoneleagh grey which is what the old ferguesson tractors were painted and very close to what the holt crawlers were painted. available in 4lt tins from any bareco stockist.

Need to be mindfull there are different Cat yellow's;

Highway Yellow, for all the early tractors when it was lead based, can still be obtained or made to match without lead.
Old Cat Yellow, lead free, came into use I think in late seventies or early eighties. (darker & more orange)
New Cat Yellow, current yellow used by Cat for their current production.

Wombat