from the government
As a result, the government runs the insurance program. You cannot buy private insurance for this as it is now illegal to sell and has been for a while. (At least it was when I bought my house in 1994 and sold it a few years later).
You don't get coverage unless you pay the premiums. But you won't get a mortgage unless you pay for coverage. As the article says, this is the “National Flood Insurance Program”. It is insurance. The program pays for itself but some years it has to play catch-up if enough claims come in at the same time.