Not sure if the following fits the bill. But run a search on Amazon.com for Olympic Dumbbell or Olympic Dumbbell Handles. These are not sold directly by Amazon but by a third party. Item description claims a 500 lb capacity, but uncertain if it corresponds to one dumbbell or split between the two (e.g. 250 lb each or 500 lb each). One of the available Olympic dumbbell description reads:
* Precision engineered, 20 inch, 12 lbs with 6 inch olympic sleeve, chrome finish.
* precision screw ends with thread locker, for long term usage.
* 500 pound capacity, sold as one PAIR. Collar not include.
Olympic 20 inch Dumbbell Handle
Olympic Dumbbell Handles sold as Pair