90-99mg is pretty much the standard dosage in most potassium pills.

Most potassium supplements are made from potassium gluconate which is only roughly 16-17% potassium. So even though the bottle may say 550mg potassium gluconate per pill, only around 90-99mg is potassium.

The pills would have to be fairly large to get more potassium per serving. Your probably better off finding the cheapest potassium supplement and just taking multiple instead of searching for a higher dose per pill.