I think there's a bunch at eBay for sale presently. Just search for "Peugeot" under the "sporting goods" category. You might not find an exact decal set for a PSV, but some of the lion logo decals were shared between models. You might just have to just find the right set with the same color/size lion decal for your bike.
BTW, that's the head tube badge (82/83 model?) you are showing on your pic, not the side seat tube decal.

Chombi