You can get resistence against X from potions and you find a lot of those in the game and they last until you rest.
Based on this
post, there appears to be 8 in the game. In my current Patch 4 "100%" save I have 6. I likely missed a couple, or there may be a degree to RNG when it comes to loot. Regardless, it's a decent amount if you're only using it for 1 character, but 8 potions will only last the party for 2 rests.
Note, you also cannot stack the resistance potions (but it does work with the spell). So in the EA right now, you can cast the level 2 Protection from Poison spell and drink any other Elemental potion to have 2 resistances.