You can get this early on. During the boss in Mission 3, simply stand there and die. Select to be revived, then mash X to get your life back. You can repeat this 3 times, and then you'll have to re-start the checkpoint (beginning of the boss battle). Just repeat, until you rack up 20 revives.
I didn't "exactly" stand there. I just haven't gotten the hang of it on Hard yet, but got the achievement after reviving and restarting multiple times.
Also, a tip about the reviving process itself. I found that the higher you go towards 100%, the faster it wants you to be pressing X. So if you start out mashing it like mad, it's actually more difficult to reach 100%, and you might even end up failing. Once I figured this out, it helped tremendously. Mash it at about half the speed you normally would until it's up around 50-60%, then start going faster. Seemed to work much more reliably that way.
Unless you're playing on Easy *and* are very very good (which seems like a strange combination), you'll need to be revived more than 20 times just through normal gameplay. So if you're not in a rush, there's no need to grind for it earlier. Just buy plenty of Mika tickets at the store between missions. I have gone through twice so far, once on Hard and again on Very Hard, and have used around 80 Mika tickets to revive.