"Original No Salt" is my secret weapon! It's potassium salt, KCl. That's the brand name. I found it at Walmart where the regular salt is located. I call it a secret weapon because I can add 1/4 tsp of this to my Low Salt V8 juice (8 oz.) and wind up getting a whopping 1500 Mg. of potassium in a mere 50 calories.
I hear ya about "beet greens". Personally I've never seen them, but I haven't looked either. But they are listed in the database here. And yes, apparently they are the green part of the beet:
Swiss chard is a pain. Too expensive, a pain to cook it down. I get a whopping 5 grams of potassium a day just by eating a sweet potato, frozen broccoli, a few bananas, and possibly some "No Salt" sprinkled on some foods. I've also switched to raw spinach salads. That's it, raw spinach and Newman's Own mild salsa (extremely low calorie and very low sodium).
I used to do Potassium supplements, but now since I've changed my eating habits I don't need them any more. They are 99 mg. per tablet due to the government not wanting anyone to overdose if they accidentally take an entire bottle. Potassium in high levels all at once can stop your heart.
If you start eating sweet potatoes you won't have any problem with your vitamin A at all either.
As far as magnesium, very wise to be monitoring it. Do a tag search for magnesium and you'll find some tips on how to get more.