Thanks Roger. yes, in North Norfolk in the UK. Actually - the internet is an extraordinary thing and shortly after asking you the question, I discovered two counterweights on sale and listed as “Weights for Victorian Bellows”. They reckoning the weight is 53lbs (24kg) for transport, so if that’s each then quite a lot heavier that yours, but I suspect it is for both. Anyway - I bought them, so we’ll see when they arrive. The leather is in good nick, having been replaced before I bought the forge.
Thanks for letting me know.