OH WAIT I JUST GOT THIS! I know it's not super reliable, but I got a contract with Monizmed. They sometimes give you drugs as payment / reward for completing their contracts, and I just got rewarded Edurance+. This still sucks tho, cuz it's not guaranteed :(
Viewing post in Endurance +
I believe this is now the intended method to get Endurance+. From the .90.1 change log: https://incontinentcell.itch.io/factorial-omega/devlog/861574/090-update-release...
- Endurance+ will no longer be purchasable from the shop. You can only get it from Monizmed contracts.