Where can I find central heating system with radiators?
You should be able to find them in any of the original colonies in colder climates, as they're needed for restoration work in older homes.  (so, eastern seaboard, from Maryland to the north)

American radiators tend to be heavy steel or iron and gravity fed, with larger pipes that I don't believe are as efficient as those found in areas like Germany.  My neighbors are currently going through a remodel of their home (1940s construction, in Maryland) got theirs from an architectural salvage place.  The burners (oil in their case, and in my home), you can still get new so are easier to replace.

Contact your local plumbing supply store; if they can't tell you where to find radiators, their customers (plumbers &amp; pipe fitters) might be able to.

You might also find the 'baseboard heating' where there's a copper pipe with fins attached that run along the whole wall of a room.  If you just want the non-drying qualities of radiator heat but can't find radiators in your area, this might be an alternative.  (I've never seen fan-assisted models in the US, either, but I'm guessing if they have them, it'd be in the northeast.