Replacing a 4 metre long radiator.

Hi

A search on Screwfix and a few other likely outlets brings up nothing like that size of a radiator (it runs off the central heating boiler)

Would it be more or less impossible to replace?

I don't think there would be any point in getting one made especially (if even possible) as the price would surely be a lot

For the future I have a few 3 metre radiators that (if they go) may be equally hard to replace.

Or are there firms that might routinely supply that kind of a product?