You can't collimate a diverging beam to infinite range perfectly, you can focus it but you have to have a defined end point and allowed beam width (to avoid confusion with barriers)
The simplest way to collimate a diverging source is with a tube made out of a material which will absorb the frequency that the source produces. You lose a lot of amplitude this way though; you could diverge it further with one lens, refocus it down to a smaller point with a second lens, and use a third lens to refocus it from the smaller point outwards to the target distance, but this is optically complex.
A LOT more details on your part would be required to recommend anything specific. Specifically you'd need to know the exact divergence of the beam you have and it's width, and define desired target distance.
Keep in mind, a laser range finger over 1km is going to be virtually useless if you don't have some really high powered optics to aim it, and the optics and the laser source need to be calibrated for accuracy. It's also going to need a pencil thin beam that is highly collimate, and this is not easy.