The filename varies depending on how you have it set up. As mentioned, you can save it as anything. In my case, the users list is in Users.ini, separate from the variables and whatnot.
You would be better off separating it from the variables into a new file, then use /filter as mentioned. You can sort using any token, so sort it by what is after the = if you're using .ini or else just use .mrc as mentioned to make it even easier.