Thanks Malcolm. I know there are none left here (Raparee did very good work, but they're gone). I also know there are quite a few in the UK but any of the well known places I've asked so far have been so-so about whether they could match the old seat stays. I suppose I'm looking for recommendations for somewhere that will share my enthusiasm for this old frame!
I also know that this is not really worth while from a purely financial point of view, but I want to have a go anyway. As you've realised, I had a look at the possibilities before, and didn't get anywhere. I've decided to try again.