You can get them at any drug store. My son has tubes in his ears and wears them during swim lessons. "Mack's" has cool orange ones. They come in a small case with approx 6 pairs- though they can be reused multi times.
They will be in the isle with ear drops, eye drops, etc. They also have soft cone shaped plugs that may be easier on/off and more comfy. DS uses these for daily showers. He is not fond of having the wax ones pushed in to fit the ear canal but uses them swimming because they are much easier to find in the pool if one falls out.