Hi Oliver, welcome to the site.
As has been said, do a search on threads and you'll find a great deal of information, but in essence, I think you are looking for a 50 or 56mm objective and a varimag up to 16 or 20?
I'd buy second hand and I'd buy the highest quality you can lay your hands on.
Premier Scopes - Swarovski, Zeiss, Leica, Kahles, Nightforce
First Rate - Nikon, Minox, Leupold, IOR, Pecar
and of course there are others.
E t R