It's been my experience that "when cheap Chinese electric devices fail" the best course is to just replace the "designed to be disposable" devices....
That said, you might be able to remove the light from the ceiling, use some spray contact cleaner to clean the contacts, or you might find a weak spring on the switch. I'd guess finding a replacement part for the switch would be impossible, and at that point, you'll be replacing the light.
At "around $5-10 each" I find it's easier, less hassle and, in the long run, cheaper to just replace them without even trying to repair or troubleshoot the sticking switch. Now, if you're bored or MacGyver.....