Actually there are three "Allis Chalmers Orange" colors. Old stuff, like your B was Persian Orange No. 1; Persian Orange No. 2 starting about 1960; and "Corporate Orange" after 1977. Each new color was progressively darker and redder. Most tractor and implement enamels sold as "Allis Chalmers" orange are Corporate Orange. TISCO has an Allis Chalmers Orange that is lighter and more yellow than Corporate Orange and is a better match for the Persian Oranges, although I'm not sure if it's supposed to match No. 1 or No. 2 or something in between. TISCO (Tractor and Implement Supply Co.) is an aftermarket parts distributor and there stuff is handled by many dealers. You can buy TISCO stuff from Walt's Tractor Parts on the "parts and supplies" page at this site.
Fanatics doing pure original restorations generally use automotive paints to get a color match.