Hi Jim,
K�¶slin, (Koeslin), is now called Koszalin and is in the part of Poland that used to be in German Pomerania before the end of WW2. I've attached a pre-war map to show where it is. On the map it's in the dark shaded area. Roughly speaking it's on the Baltic coast not far from Gdansk, (Danzig as was).
The Landjaegerei was a police formation - rural as far as I know - but there are people who post here that know a lot more about this than me.
Any chance of some photos of your Luger - especially the unit marking?
Cheers,
John