Well, the only compatability issues would be thread pitch on the connector rings and heat output.

I believe that the connector rings (proper terms escape me right now) are pretty much standard across the English speaking world.

Why do you want to replace the radiator?

Also, Burnham makes radiators in the US. Plus you might try getting one from a salvage yard.

When I've needed used radiators I've talked with heating contractors or workers from the local gas company. They always seem to know where there is a cellar full of them from a system that they have just converted to baseboard heaters. And, the price is $50-$75 each rather than $500-$800 for a new one. If a used replacement doesn't leak it will probably be good for another 100 years.

Burnham makes cast iron radiators that are made in the US. They have new plain jane radiators (see the "slenderized" line), and also more ornate radiators (see the "classic" line).
http://www.burnham.com/radiant_products.htm

You'll want to figure out your current radiator's output capacity. Once you know that, you can then judge if you want to get a replacement radiator that has less, equivalent, or more capacity depending on how well or how poorly the current radiator heats the room. Of course if the current radiator is heating the room poorly, there could be plenty of reasons as to why other than assuming it is undersized.

Bearing that in mind, here is a site to help calculate the capacity of an existing radiator:
http://www.colonialsupply.com/resources/radiator.htm

The Burnham site has specs (link says "literature (pdf)" and that will help you find the physical size radiator you need to match the current capacity.