You want to get your 4/5* heroes ascended, right? The only option in the current game mechanics is to gather more ascension items.
Surely, this has been suggested before, but Why not use the existing shop and have ascension items appear for purchase for very limited time windows?
This gives you the opportunity to get that final Mystic Tonic and Damascus Blade, while giving SG another mechanism to encourage people to go into the shop. How is this not a thing yet?