Where can I buy slim short tail casual shirts?

[Liquidus]

Hello, I have been looking for slim casual shirts (preferably button-down) that I can wear untucked. From what I've learned, that means it needs a short square tail. However, for some reason, I have not been able to find these at any of the online retailers I have looked at. I have looked at Brooks Brothers, Ralph Lauren, J Crew, TM Lewin, Charles Tyrwhitt, Land's End. I'm guessing they don't really cater to the type of people that would wear a shirt untucked. Does anyone know where else I can find good quality, short tail shirts? Thanks for the help.