How common are Chinese swords with bent blades?
 

How common are period sources stating Chinese blades bending in combat, or examples of antique Chinese swords with bent blades? Swords bending were a common occurrence elsewhere in the world, I’m wondering if this phenomenon was also recorded in China?

Really unusual question. With bronze weapons, it was usual as I understand that these blades would bend, and had to be returned to shape. In much later years where blade flexibility was of course important bending blades was a common test.
What exactly is being sought here, what period etc.

Pretty common I'd presume. As older weapons many are only edged quenched and many are laminated on an iron blade.
I've seen plenty with bends

Agreed, I've seen a few with bends. It's like Julius stated.