I have, 20 years ago. Bought them from a farmer's market stall and all six were double yolks. Went back week after week but sadly never again. There is an explanation for it but I can't remember it.
I used to keep chickens and we quite often had double yolkers, at the local market you could buy double yolkers any time, but they did charge a bit extra. The eggs can be scanned with a candler to detect them.
I bought a box of extra large eggs from the supermarket recently (it's all they had) and all were double yoked. I assumed at the time that something about the double yoke made the egg grow bigger.