A lot of the area around Somerset is mostly Pennsylvanian sandstone from what I've seen-no chert. But the Mississippian limestone formation is right under the sandstone, so if you can fine some exposed limestone formations, you can probably find chert. Around the lake might be a good spot to try. I looked around the upper end of the lake around the Rockcastle River arm once, but all the bedrock around there was still sandstone.