And aphids from ant hills give some. Also if you get lucky while fishing, the plaice fish give perception. I don't know where specifically it is easiest to catch them though (river vs lake, deep vs shallow, bait type, etc.)
I had issues with perc early in world but eventually we got a big farm of carrots and beetroots and perc became very easy to raise. With deer meat, bat meat and carrots/beetroot, you will get instant perc FEPs.