Get Mercs 2 - it tosses out Achievement points like a piñata spews candy.
Just make sure you unlock all the landing pads before choosing whether to help one faction over the other get a nuke. I'm SOL because now one hates me and there's no way to get anymore missions to further unlock their landing zones and bases 
That /does/ suck.
Of course, you're only talking about the endgame choice interfering with one of the Achievements, which is pretty minor. I suspect you could have used multiple save-points (admittedly slightly less convenient in Mercs 2 than, say, Fallout 3) or could re-play and unlock them all from a new game in about 4 hours.
It's minor. I just wished I would have read online beforehand. It's most definitely not worth going through again just to get the achievement haha. I was so pissed to see that Obama and Palin were only playable in the crappy minigames and not the main game. That still pisses me off to no end.
Actually, I still haven't found where to play them. I assumed they were skins that you changed into at the wardrobe, and only in the DLC. Where are they? Also, what minigames? The factions non-mission stuff, which you get like 2 or 3 stages of? (e.g. Delivering parrots for Jamaicans)
I have to play the whole thing through again eventually, because some trigger-happy shitheel whacked one of my HVTs while I'm still going for the "Aces High" (no HVT killed) Achievement.