After several enquiries, I was told by a friend in the UK who owns a small electrical goods shop that manufacturers generally will not now supply replacement motor brushes. This applies to all major makes it would seem. Given that we are constantly being bombarded with demands from all quarters to 'save the planet', one has to question the wisdom of dumping perfectly good motors for the lack of a couple of bits of carbon. It is an obscenity of the first order but obviously very profitable for the appliance makers.
Not to be beaten, I went to a hand tools repairer (industrial angle grinders, etc.) and asked them if they could supply some thing similar to the Dyson brushes. For a few quid they sold me some which were oversize and with a very fine file and wet-and-dry abrasive paper I ( gently!) reduced them to fit.
As for the soldering of the tail, that presented no specific problem as far as I could see. However, as one is dealing only with mains voltages, even an unsoldered connection will suffice providing the mechanical 'bond' can be made sound enough to prevent arcing.
I should remark, that first replacement of brushes did not last as long as the original brushes. I don't know why. Is it that some are slightly harder and don't wear as quickly perhaps? Or perhaps the original brushes were much longer. Does anyone know the correct length?
However, I have just had to replace the replacements and could not find any more with copper 'tails', so I have simply installed the new brushes with the springs under the brass tags and the machine is working fine. For how long though remains to be seen.
Incidentally, I did recently notice an e-bay advert for Dyson brushes in the UK at around £2.50 per pair, plus postage but stupidly did not make a note of it. The supplier did not offer a web site address but did provide e-mail and 'phone contact details for enquiries. If I find it again I will post it on this site.