You will find shirts, shorts, one pieces galore at all different places.
I have a couple of shirts I bought DS from Old Navy that are doing the trick for day camp this year, but they will be too small by our winter vacation in FL, so I need to find a new one for the winter.
Our local stores were only carrying the "zip-up" wet suit
...and of course, no one knew what I was talking about..
"Wow that would be a really great idea, ma'am"
*sigh*