Pardon me for asking but it seems I missed this being mentioned, but where are you exactly?
I’m sure pork kidneys would be amazingly cheap if I were to find them in my grocery store, but that’s one thing I don’t recall seeing. It may be available at times, but I haven’t noticed it in the offal section at Jewel or Mariano’s, and I do peruse it from time to time.
If you want fresh kidneys, or even frozen ones, you usually have to ask the butcher for them. IDK how this would work at a big-box grocery store; a butcher shop is a better bet and may even have them in the freezer. An independent shop I sometimes go to has brains, sweetbreads, chicken feet, tripe, etc. in the freezer case. They sell everything that’s legal to sell.
I, too have heard of soaking organ meat in milk, or vinegar and water, to remove strong flavors.
My grandfather wanted my grandmother to cook kidneys for him and a neighbor and she refused to even have them in the house. She was away one day, came home to find the house absolutely reeking of the worst smell! Grandpa and the neighbor decided to cook up a kidney feast for themselves, and they ate them. She said the next day both of them were deathly sick and vomiting, all day.