I finally found a reasonably local person to skim the A7 front drum. He has an industrial-standard workshop in the grounds of his house, complete with lathes, milling machine etc and the remnants of his days building (and sponsoring) race bikes, namely a couple of semi-built Goldie engines, self-built frames etc.
He trued the drum in less than 30 minutes (we went to the local cafe for a cuppa while he did it) on the biggest lathe using a roller on the tyre to spin the wheel. Sadly through age he's now selling his equipment and taking it easy, and won't be doing many/any more wheels, so I got in just in time.
Shame that, not too many old-style machine shops who have an understanding of bikes still left now.