Before deciding to grind these out, play through the campaign once (twice if you decide to split a regular run and Sniper Elite difficulty run) and do the Horde achievements with a friend or two (or even randoms). By that point you'll probably have most of the revives needed.
If you don't have the achievement by this point, either leave one or two zombies alive in a group and take it in turns to get downed and revived/draw away the zombies and revive. Or get to the first time where you meet a Chainsaw Elite. Clear out all of the other zombies and get him to down you, simply draw him away, revive your partner, then rinse and repeat.