That's a tough one, as that color is long discontinued. Most of the reference charts I have don't even show it, or show it as discontinued without any cross reference. I did find this chart:
http://www.fortunecity.com/meltingpot/portland/971/reference/humbrol.htm
You have to scroll down to the bottom of the page to find the discontinued colors. That list shows Gunze Sangyo 46 which in turn cross references to Humbrol 2 Emerald Green, so I don't know how much help that is. I used to have a Humbrol paint chart, but darned if I can find it!
I did find this reference http://france1940.free.fr/armee/colours.htm which shows H150 Matt Forest Green as the first alternative, H179 as the second alternative and H86 Light Matt Olive + H81 Matt Pale Yellow + White as a third, but doesn't give proportions.
There's also http://www.navigatorminiatures.com/product.asp?P_ID=3395&print=y but shipping a pot of paint from England might be a bit much! It also looks just a touch greeer than Model Master Olive Drab.
Hope this helps!
Bill