There are plenty of places that offer extended warranties. Generally they'll only cover a used car if it has a limited number of miles on it at the time, but thats's usually around 100k. The price you'll pay will depend on the value of the car, make and model of course, and age and mileage. They vary in what they cover, most used car warranties paying only for replacement of major items. Some don't cover repairs that are considered wear and tear, some con't cover specific parts like radiators, etc.
Whether it's a smart buy is a different question. There are plenty of scams and fly by night operations in the extended warranty business so be sure to do some research and find some reviews of the company before you do it. And consider whether the cost of the warranty, once you get a quote, is really worthwhile in relation to how much you paid for the car and what the likelihood of failure of a covered
item would be.
I'd expect you could find companies online with a search like "used car extended warranty."
(Yep... that worked.