You can stack up Perception from the following sources:
-Food (Best I can find is +2, but there might be a +3 recipe in the game I'm missing)
-Resting (There's a couple that add +2 to perception, can't remember the names or locations)
-Items
Note that each of the categories listed can only be added to a character once. While there are multiple foods that can add to a stat, only the highest food effect for a stat is not suppressed. As long as you do not rest again, you can retain an inn's bonus indefinitely, so be sure to not use Caed Nua's bed since it's generally pretty poor effects compared to almost every other inn. As with food, only the highest value of an item is not suppressed when there are multiple items on a character.
You can add Perception via enchantments on a weapon (+2), and I'm pretty sure the food and rest bonus are also capped at +2 each, meaning your total added can be as high as +6 over base. You can place this on your main character or any of your companions, if they happen to have a higher base perception.
Alternatively, you can simply "hire" a custom adventurer from any inn and make them a detection slave. I believe the highest starting Perception possible is 20 or 21, meaning you don't need to craft or anything if you don't mind temporarily losing a slot to bring them along.
Your main character in Act 3 also gains a special ability that adds +2 onto all stats except intelligence, usable once per rest. If you haven't dumped any stats, +8 generally means your main character should be able to find or complete any task if you know what/where it is beforehand, and you plan on resting/eating a lot of food between now and then.