If you’re going to swim at Colman, I’m quite certain they sell caps since Southwest sells them. I can’t think of any places near Admiral that would sell them. Next time you’re out and about, try Sylvia’s Swimwear in Bellevue or Northgate since they have the best selection.
I am sure that Coleman pool must sell them, there is also a swimwear place on Calif, right above the Blue Moon place (just South of the Radio Shack at Oregon) and they would have them too.