This can boosted fairly easily since not many people play this game anymore.
Find a friend/fellow booster or two and search for the same gametype in ranked matches. Hopefully you'll find each other relatively quickly. If not, ask the people you do find if they'd like to boost. If they don't, just avoid them in player feedback.
Once you've found your friend/fellow booster, find either a sniper rifle or the bow (each is a one headshot kill). Take turns getting headshots off of each other and the achievement should unlock after the end of the match.
If it doesn't, one of your kills may not have been registered as a headshot. Try again, and you'll unlock it eventually.