This is an FDA limit on potassium chloride supplements. Too much potassium can cause heart rhythm problems and cardiac arrest.
Some organizations propose 3500 to 4500mg as a daily potassium intake, and 98% of people do not eat this much potassium, and unless you are living on beans and beats you probably aren’t. Yet there isn’t a huge “get more potassium” movement. I wonder if those targets need reassessment.
I was once on a low potassium diet and had to avoid half the of foods I normally ate. You are likely getting enough potassium in your diet without needing any effort.
I had no problem buying potassium (gluconate) powder by the pound off of Amazon for cheap. (I am in the US.) Be careful with it because if the ratio of potassium to sodium in your blood gets too high, it interferes with the mechanism that sequences the contractions of the chambers of the heart or such.
Quite a lot of common staples (eg: potatoes, greens, vegetables, pulses) have a fair amount of potassium, if you look at the "potassium in a standard portion" column (and remember these are fairly small portions, the assumption being that a meal has a portion of several different things).
I'm not seriously suggesting we all move to 100% cardboard-tasting goo, but if you are worried about one or more of your daily intakes, this could be an easy way for some people to get a good dose every now and then (for example for lunch on weekends, I notice that I'm often in the middle of something fun and will neglect to have lunch).
Most people get enough potassium from their diet. It's easily available in larger quantities but safety is the main concern:
http://www.straightdope.com/columns/read/1364/can-salt-subst...
Nu-Salt salt substitute is 100% potassium chloride in a 3-oz container. Morton Lite Salt is a 50-50% mix of potassium and sodium salt. Both are available in grocery stores. But use with caution and usually with the advice of a physician.
11 bananas worth is about 1000 calories. So if you get about 1/2 of your calories from varied non-grain plant foods, you should be good.