You can find them at Aim Surplus, Samco Global Arms, Southern Ohio Gun, Empirearms, Allens Armory or Allens Armory there all on the net.
Now there are two different yugo sks's the model 59(M59) has no gernade launcher attachment and it looks like a regular sks. The model 59/66 has the gernade launcher on the front with a gas shutoff valve on the gas port housing. If the 59/66 won't cycle you have to checkout the gas shut off position. As far as price it depends on the condition I think they still run from $100 to $175 and from a shooter condition to a unissued condition. Remember the yugo's don't have chrome lined bores so clean them good after shooting corrosive ammo.