Goodgulf:
Another one: "In the Family Way" presented several opportunities for the newly married wife played by Hayley Mills to go over a knee. Her husband's, her father-in-law's, maybe her mother-in-law, clearly her new brother-in-law, and several others. She even shows off her spankable butt in a bath tub scene (one of the many times she should have been spanked).
So glad you mentioned that - one of the best films of all time in my opinion. I'm not sure about your "several opportunities" though, as Hayley Mills' character was quite a saint really. But certainly in that scene near the end where her husband gets angry and throws her down on the bed, a spanking could have been introduced very plausibly. As for the bathtub scene, I think the Boulting Brothers (bless them) liked to sneak a little bit of nudity past the censors. I recently watched "I'm all right Jack" which starts and ends in a nudist colony. In the final scene Ian Carmichael is chased towards the horizon by a gang of naked women.
Alef:
I think the 19th century would provide many good candidates from the novels of Jane Austen and the Brontës (and, of course, from their many latter day followers).
There are quite a few spankers in Dickens (Mr Murdstone, Wackford Squeers, Pip's sister in law) but unfortunately not very nice ones!