Ultra evolutions

Working on my second ultra evolution and need to know where the silver tower is located

Silver tower? What are you trying to obtain?

Hit the Dungeon in Stage 4 …usually they appear .

Oh, silvermouths? If you check this post ever again:
Online -> Ultra evo & events -> Ingredient missions -> Mouths of Truth
OR
Online -> Missions -> Chapter 4 -> Choose a temple -> Go to the dungeon. Sometimes spawns in wild battles.