funnily enough there is only one natural working monopoly I know. Bear with me, as this is going to get dutch:
There where about 5 comapnies making cocos-bread (slices of processed coconut) which produces about 20M slices a year together.
The market died when coconut prices grew about 5 years ago, this was a local and quite short shortage, but it disrupted the price so much that 3 of the 5 companies went under.
One of the other two companies decided it wanted to buy the other company, since otherwise they'd both die. The consumer protection agency (think FCC but working kek) was like> no nigga
But the two companies almost died, and the ACM (again, FCC but working) allowed them to merge.
Business has been on a really really slow rise, but since the netherlands is litterally the only place coconut-bread is being eaten there is no way another company can compete without dying both.
And thus a natural monopoly was born.