Sorry if this is the wrong place to post and yes I've searched for hours here and on the internet. Anyway... This likely isn't new news but I found that Krylon Ultra-Flat K04293000 Camouflage Made with Fusion for Plastic Technology Spray Paint, Olive, 11 Ounce, is almost a perfect match with Magpul OD Green. I had some Troy OD Green rail covers that are way lighter than Magpul's and bought three different spray paints to see what was closest. One good coat of the Krylon and I almost can't tell the difference - just make sure it's the exact one above. Clearly, some folks don't like Krylon but I've never had an issue with it - I'll post a follow up as to how it works out down the road.
The next closest was the Rustoleum camo green but it's a little too grey (it was still fairly close). See pics below but know pics never match reality - it is super close. The magazine is more of a satin finish, the handguards are now flat - I suppose if you're pickier than me you could add a satin clear coat. Of course, none of my Magpul OD Green exactly matches (handguard, grip and mag) so this works great. I honestly don't think you'll get much closer than this for basic spray paint at about $6 and I'm pretty picky. I'll also note that I'm painting plastic rail covers and not metal. Just shake it up good and follow the instructions - if there's oil or CLP on it the paint won't stick.
Hope someone finds this useful.