You can buy a three-jaw chuck in many places, such as Grizzly: http://www.grizzly.com/catalog/2016/main/383?p=383 http://www.grizzly.com/catalog/2016/main/383?

You can buy a three-jaw chuck in many places, such as Grizzly: http://www.grizzly.com/catalog/2016/main/383?p=383 http://www.grizzly.com/catalog/2016/main/383?p=383 It should be relatively simple to retrofit one of these to an existing brace with a different chuck. If the brace doesn't have a matching taper, a machinist should be able to turn it or put a thread compatible with a chuck on it.