Thanks for all the contacts people. Richard Weber at Eggesford came up trumps with a full set of four which will allow me (read Vintech)to fix the three low compression pots (the good one was rebuilt last year) and get a spare cylinder ready for potential disasters. Thanks again all.
BlueRobin Annie the Auster is indeed up for sale. The most serious potential buyer was put off (and I can't blame him) by the propensity of the No.1 cylinder to oil it's plugs. This will be cured by the top overhaul that I can now get done!