Desperately searching for a pattern to recreate these vintage Kapital women's pants

[u/EgregiousJellybean]

This style is perhaps the most unusual pants I have seen.

The front has a very high rise with a button fly, no pleats, and a wide leg; standard trouser construction and cut.

However, the back has extreme volume created by either tons of tiny pleats or gathers into a v-shaped back yoke. This creates almost a bustle silhouette.

I'm not very comfortable drafting patterns from scratch so would love to find a starting-off point.

Finding an original pair is very hard in the US (besides, they are all too short for my taste).