You asked. I answered. Twice, in fact. I've done part of your homework for you. Now, if you want to support your (apparent) claim that the Norks don't realistically threaten Seoul, you'll have to do the rest of the heavy lifting yourself.
What you CAN NOT do is claim that no artillery with range >= 35 miles exists. You now know that it does. Furthermore, if you count rocket artillery (Does the target know the difference when it's getting blown up?), the range is much greater than your 35 mile threshold.
I await your well sourced essay on the quantity and quality of Nork artillery.
Are you holding your breath?