The new version of Soldat, 1.4, has a completely new lobby server that fixes the problems of there being "some that don't always turn up in the server browser."
There is a way to query servers directly (look in the stickies and the other parts of the Developer's Corner, but this won't help you create a list.
I suggest you wait until 1.4 is out to see if what you wanted to do is really necessary. The new lobby has been written from scratch intentionally to fix these kinds of problems.