Sounds a good idea. Have rung up a few model makers to no avail. For one I do not know the diameter of the pipe to which it would need to be soldered onto.
And it seems, if a suitable valve was available, delivery is another factor. Many parts seem to be in very short supply.
So am going to go with blanking it off. At least by doing this I can at least get the radiator fitted and get out on the road, whilst we have the odd day of sunshine.