looking for late night kgirls
after midnight

finding one after midnight.  You may have a better chance with a Chinese provider at a Corgs but service and looks may not be what you want.

Plenty of kgirls work till well past midnight in Vegas

Kgirls work until two or three in the morning.  First appointment of the day is rarely before noon, sometimes mid-afternoon.  

You just have to ask.  Usually, if it's been a slow day, they will ask the girls, and one or two will usually stick around.  If you ask too late, then they've already started winding down.  I've gotten sessions as late as 2am.