Missed chaos flame for level 4 to 5 upgrade any recourse?

I beat the last story boss, but in lost items no chaos flame shows up (some traveler items did though) and my blades of chaos are stuck on level 4. Am I permanently gimped or can I grind up enough of the funny resource to buy enough chaos flames to reach max level for the blades?

I backtracked to the Tyr's underground move the giant chains part, but can't go back into the Jotunheim tower either. Didn't find a convenient chaos flame lying on the ground.

The final upgrade for your weapons doesn't come from a normal boss drop like all the previous materials. Instead you will need to trade a resource from "post game" activities to unlock it. Doing these will each unlock a Playstation trophy as well.

For level 6 of the Leviathan Axe you will need a Chilling Mist of Nifheim which you can find by

Unlocking the workshop and opening the third golden chest from the left inside there.

This can be traded at a shop for a Frozen Flame and upgrade the axe to it's final level.

For level 5 of the Blades of Chaos you will need to get a Raging Inferno of Mespelheim which you get by

Beating all six trials of Mespelheim and defeating the Valkyrie.

And again you go to a shop and trade it for the final Chaos Flame.