I know that Novaks and Heinie at least made drop in sights for the XS series (dont know if they still do). Someone on the board may know of others. You may also have tritium installed on the original sights.
I got off my butt and did a little research and found the answer to my own question. I will share it here in case anyone else wants to know.
I called Novak and they were worthless and sounded pretty unknowledgeable. They said that they were not familiar with the now discontinued XS Model and had no clue what dovetail it used and had no way of finding out. They said that they would have to see the slide to know whether they had a sight that would fit it or not. I nicely said thank you and hung up then told myself that they lost a sale whether they have one or not. I hate people who don't know their own product they are paid to sell.
I called Heine and they were very pleasant and helpful. She knew exactly what I was talking about when I said XS Model and she told me that they used to make a set for that gun but discontinued it when Colt changed their sights ala the XSE Model. She said that she might have some still in inventory but she doubted it. She said that she would check and call me back tomorrow.
I called Trijicon and they also were very pleasant and helpful. They too knew exactly which gun I spoke of and said that the sights they catalog as "for Colt Enhanced Models" fit the XS guns. I clicked on a pic of these on their website and they look to be the same size/shape/configuration as the sights on the XS. The model number is CA22. They are $120 retail and can be ordered direct for that or your local dealer can get them much cheaper if they will pass their savings on to you. If you want them installed they will do that for $30 including return shipping. Also they discount 10% for law enforcement if that applies to you.
By the way, I don't even have an XS model. I posted this question and made the phone calls for a friend who does have one and wants night sights.
Hope this research helps somebody besides me and my friend.