Ranger green is no longer considered a mil spec color, that being said they do have it available, but like the majority of their colorways, requires an order and then production.
The color index is read by color number and prescribed zone. I.e., 580 is YKK for black. So on the index find 580 in the column that says 'Color No.'. 580 is located in 'Index No.' "AA-19." On the actual color card find column "AA." On the far left of each color swatch page is a column with numbers 1-20. So take that number '19' on the far left of the page. Then follow row '19' to the right until you hit 580, that is color 580, black.
A lot of the mil spec colors are not on the card, they are commercial. For example D334 is Coyote, D247 is the CADPAT used with the TW color equipment. Y0978 is Tan499. Y9078 is a fire engine red, etc. The easiest way to get the codes is to emai YKK or a YKK distributor.