I ve been googling it and apparently Lapras and Ezeggutor have the highest chances of having full Hp stones setups. But lapras is low encounter rate and exeggutor has lower chance of having full hp(about 4%).

Even worse is Ive been farming exeggcutes and he barely spawns even tho its supposed to be 48%chance. I've tried for about 2 weeks now, I get Paras more often than not.

Is there anything I could be doing differently?

Edit: I got lucky and got a Pinsir with 8 Power slots and one Multislot

And also an Articuno with 3 HP slots and the rest Multilsots

So I have done bith acheivements in about 3 days just getting random luck lol. Hope this info will be helpful to someone...